DESCRIPTION Title of Invention ORGAN REGENERATION METHOD UTILIZING iPS CELL AND BLASTOCYST COMPLEMENTATION Technical Field The present invention relates to a method for producing a desired cell-derived organ in vivo using an iPS cell. Background Art In discussing regenerative medicine in the form of cell transplantation or organ transplantation, expectations for pluripotent stem cells are high. ES cells established from the inner cell mass of blastocyst stage fertilized eggs are pluripotent, and therefore used in various studies on cell differentiation. Development of differentiation control methods of inducing differentiation of such ES cells into specific cell lineages in vitro is a topic in the field of regenerative medicine research. In the research on in vitro differentiation using ES cells, differentiation into mesoderms and ectoderms, such as hemocytes, blood vessels, myocardia, and nervous systems, which differentiate during early embryogenesis, is likely to occur. However, there is known a general tendency that differentiation into organs directed to the formation of complicated tissues through intracellular interactions during and after the middle embryogenesis is difficult. For example, a metanephros, which is an adult kidney of mammals, develops from intermediate mesoderm during middle embryogenesis. Specifically, the development of kidney is initiated by the interaction between two components, which are a metanephric mesenchymal cell and a ureteric bud epithelium. Finally, the adult kidney is completed through differentiations into a number of types of functional cells, which is as large as dozens and cannot be seen in other organs, and through the formation of a complicated nephron structure, which is mainly composed of a glomerulus and a renal tubule, as a result of the differentiations. It is easily inferred from the timing of kidney development and the complication of the process thereof that induction of a kidney from ES cells in vitro is an extremely labor-intensive work, and the induction is considered to be actually impossible. Further, identification of somatic stem cells in organs, such as kidney, has not been established yet, and it has started to be revealed that contribution of bone marrow cells to the repair processes of injured kidney, which was once used to be actively studied, is not very significant. When a pluripotent ES cell is injected into the inner space of a blastocyst stage fertilized egg, a resulting individual forms a chimeric mouse. There has been previously reported a rescue experiment of T-cell and B-cell lineages by blastocyst complementation, to which this technique is applied, the rescue experiment being carried out on a Rag-2 knockout mouse deficient in T-cell and B-cell lineages (Non-Patent Document 1) . This chimeric mouse assay is used as an in vivo assay system for verifying the differentiation of the T-cell lineage, for which no in vitro assay system is available. However, even if such a technique is found to be available for a certain organ, it is difficult to predict whether the technique will actually be effective in other organs, because of the difference in the role of the organs in the living body, for example, the difference in fatality or the like resulting from the absence of the organs. Various factors also affect the validity of the technique. In addition, the deficient genes of the organ deficiency model selected in this instance are also an important factor. This is conceivably because it is required to select transcription factors that are essential for the function of the deficient genes during the development process, particularly for the differentiation and maintenance of stem/precursor cells of each organ during the process of organ formation. It is expected that when a model representing organ deficiency caused by the deficiency of a humoral factor or a secretion factor is to be used, only the factors supposed to be released are complemented by the factors released from the ES cell-derived cells, resulting in a chimeric state at the organ level. Accordingly, selection of an appropriate model animal for an organ is the key factor in the present invention. In considering the application to other organs, it is thought to be difficult to use a model representing the same phenotype as that of the present invention with respect to other organs. The present inventors have filed an application PCT/JP2 0 0 8/5112 9 as an organ regeneration method. In addition, induced pluripotent stem (iPS) cells have recently drawn attention (for example, Non-Patent Document 2) . The iPS cells are regarded to have equivalent functions to those of ES cells. Citation List Non Patent Literature NPL1: Chen J., et al., Proc. Natl. Acad. Sci. USA, Vol. 90, pp. 4528-4532, 1993 NPL2: Okita K et al., Generation of germline-competent induced pluripotent stem cells. Nature 448 (7151) 313-7, 2007 Summary of Invent ion Technical Problem An object of the present invention is to provide a technique for organ regeneration using a readily preparable induced pluripotent stem cell (iPS cell), the technique being suitable for industrial application. Specifically, the object is to provide a technique for regenerating an "own organ" from a somatic cell, such as skin, depending on the circumstance of an individual. Moreover, another object is to conduct research and development using organs derived from various genomes , the organs being provided by carrying out the present invention by way of producing an induced pluripotent stem cell (iPS cell) from a cell having a target genome. Still another object is to avoid an ethical problem that has been a problem in ES cells. Solution to Problem It has been discovered that, in a blastocyst complementation method, a next generation is born when a deficiency of an organ, such as pancreas, is complemented by injection of induced pluripotent stem cells (iPS cells) into a developed blastocyst, and further discovered that a transgenic animal having the pancreas thus complemented can transmit its phenotype to the next generation as a founder. These discoveries have revealed that organ regeneration can be accomplished by using such a founder. Thus, the present invention has solved the above-described problems. In the present invention, it has been discovered that a litter can be efficiently obtained using founders obtained by transplanting induced pluripotent stem cells (iPS cells) as pluripotent cells into knockout mice and transgenic animals (for example, mice), which are characterized by having a deficiency of organ, such as pancreas, so as to complement the pancreas. In the present invention, it was found from the result of genotyping that even if induced pluripotent stem cells (iPS cells) are used, knockout mice each with a pancreas complemented grow to normal adults. The complemented knockout (hereinafter, also referred to as " KO") mouse was expected to be theoretically a KO or hetero individual at a probability of 1/2 according to Mendelian inheritance, as being derived from breeding between a hetero mouse and the KO which is capable of transmitting its phenotype to the next generation as a founder. This was found to be as expected in reality. From this, it is possible to obtain a KO individual at a probability of 100% in the next generation from breeding between KO individuals in which pancreas has been complemented. Therefore, it is expected that analysis using KO individuals will be able to be carried out significantly more easily. Meanwhile, in a conventional method for producing a transgenic (Tg) animal, a transgene for inducing a deficiency of an organ is introduced into an egg cell followed by transplantation of a resulting egg cell. In a relatively new method, a next generation is born when a deficiency of pancreas is complemented by injection of ES cells into a developed blastocyst . It was revealed that in both of the methods , induced pluripotent stem cells (iPS cells) can be used. Furthermore, it was discovered that a transgenic animal with a pancreas thus complemented by use of induced pluripotent stem cells (iPS cells) is also capable of transmitting its phenotype to the next generation as a founder. Thus, it has been revealed that organ regeneration can be carried out using such a founder obtained by use of induced pluripotent stem cells (iPS cells), as well. It should be understood that, once the method of the present invention is found to be applicable to a certain organ, appropriate modifications on the basis of previous successful cases can be applied to the organ. The reason for this is as follows . If an appropriate defective animal is available, a similar method of analysis can be applied thereto using fluorescent-labeled iPS cells (derived from fibroblast collected from a skin or tail, for example) or the like as indicated in the present description, so as to reveal whether a thus constructed organ is derived from the host or from iPS cells or the like. This allows a judgment whether organ construction has been successful or not. Thus, it should be understood in accordance with the same theory that a next generation animal can be reproduced. Therefore, the present invention provides the followings. In one aspect, the present invention provides a method for producing a target organ in a living body of a non-human mammal having an abnormality associated with a lack of development of the target organ in a development stage, the target organ produced being derived from a different individual mammal that is an individual different from the non-human mammal, the method comprising the steps: a) preparing an induced pluripotent stem cell (iPS cell) derived from the different individual mammal; b) transplanting the cell into a blastocyst stage fertilized egg of the non-human mammal,- c) developing the fertilized egg in a womb of a non-human surrogate parent mammal to obtain a litter; and d) obtaining the target organ from the litter individual. In one embodiment, the iPS cell is derived from any one of a human, a rat, and a mouse. In one embodiment, the iPS cell is derived from any one of a rat and a mouse. In one embodiment, the organ to be produced is selected from a pancreas, a kidney, a thymus, and a hair. In one embodiment, the non-human mammal is a mouse. In one embodiment, the mouse is any one of a Sall1 knockout mouse, a Pdxl-Hesl transgenic mouse, a Pdxl knockout mouse, and a nude mouse. In one embodiment, the target organ is completely-derived from the different individual mammal. In one embodiment, the method of the present invention further comprises a step of bringing a reprogramming factor into contact with a somatic cell to obtain the iPS cell. In one embodiment, in the method of the present invention, the iPS cell and the non-human mammal are in a xenogeneic relationship. In one embodiment, in the method of the present invention, the iPS cell is derived from a rat, and the non-human mammal is a mouse. In another aspect, the present invention provides a non-human mammal having an abnormality associated with a lack of development of a target organ in a development stage, the mammal being produced by a method including the steps of: a) preparing an iPS cell derived from a different individual mammal that is an individual different from the non-human mammal; b) transplanting the iPS cell into a blastocyst stage fertilized egg of the non-human mammal; and c) developing the fertilized egg in a womb of a non-human surrogate parent mammal to obtain a litter. In another aspect, the present invention relates to use of a non-human mammal having an abnormality associated with a lack of development of a target organ in a development stage, for production of the target organ using an iPS cell. In another aspect, the present invention provides a set for producing a target organ, the set comprising: A) a non-human mammal having an abnormality associated with a lack of development of the target organ in a development stage; and B) any one of an iPS cell derived from a different individual mammal that is an individual different from the non-human mammal, and a reprogramming factor and, if necessary, a somatic cell. In another aspect, the present invention provides a method for producing any one of a target organ and a target body part, the method comprising the steps of: A) providing an animal which includes a deficiency responsible gene coding for a factor which causes a deficiency of any one of an organ and a body part and gives any one of no possibility of survival and difficulty in survival if the factor functions, and in which the any one of an organ and a body part is complemented hy blastocyst complementation, the deficiency responsible gene coding for a factor which causes a deficiency of the any one of a target organ and a target body part ,- B) growing an ovum obtained from the animal into a blastocyst; C) introducing a target iPS cell into the blastocyst so as to produce a chimeric blastocyst, the target iPS cell having a desired genome capable of complementing a deficiency caused by the deficiency responsible gene; and D) producing an individual from the chimeric blastocyst, and then obtaining the any one of a target organ and a target body part from the individual. In one embodiment, the method of the present invention further comprises a step of bringing a reprogramming factor into contact with a somatic cell to obtain the iPS cell. In one embodiment, the step D) includes developing the chimeric blastocyst in a womb of a non-human surrogate parent mammal to obtain a litter, and obtaining the target organ from the litter individual. In another embodiment, the target iPS cell is derived from any one of a rat and a mouse. In another embodiment, the any one of a target organ and a target body part is selected from a pancreas, a kidney, a thymus, and a hair. In still another embodiment, the animal is a mouse. In another embodiment, the mouse is any one of a Salll knockout mouse, a Pdxl knockout mouse, a Pdxl-Hesl transgenic mouse, and a nude mouse. In still another embodiment, the any one of a target organ and a target body part is completely derived from the target pluripotent cell. In still another embodiment, the iPS cell and the non-human mammal are in a xenogeneic relationship. In still another embodiment, the iPS cell is derived from a rat, and the non-human mammal is a mouse. In another aspect, the present invention provides a set for producing any one of a target organ and a target body part, the set comprising: A) a non-human animal which includes a gene coding for a factor which causes a deficiency of any one of an organ and a body part and gives any one of no possibility of survival and difficulty in survival if the factor functions, and in which the any one of an organ and a body part is complemented by complement; and B) any one of an iPS cell derived from a different individual mammal that is an individual different from the non-human mammal, and a combination of a reprogramming factor and, if necessary, a somatic cell. In one embodiment, the non-human animal and the iPS cell are in a xenogeneic relationship. In the present invention, cells to be transplanted are prepared in accordance with the species of an animal for the organ to be produced. For example, when a human organ is to be produced, cells derived from a human are prepared. When an organ of a mammal other than human is to be produced, cells derived from the mammal are prepared. In the present invention, as the cells to be transplanted, induced pluripotent stem cells (iPS cells) can be used. The organ to be produced in the method of the present invention may be any solid organ with a fixed shape, such as kidney, heart, pancreas, cerebellum, lung, thyroid gland, hair, and thymus. Preferable examples thereof include kidney, pancreas, hair, and thymus. Such solid organs are produced in the body of a litter by developing totipotent cells or pluripotent cells within an embryo that serves as a recipient. The totipotent cells or pluripotent cells can form all kinds of organs by being developed in an embryo. Accordingly, there is no limitation to the solid organ that can be produced depending on the kind of the totipotent cells or pluripotent cells to be used. Meanwhile, the present invention is characterized in that an organ derived only from the transplanted cells is formed in the body of a litter individual derived from non-human embryo that serves as a recipient. Thus, it is not desirable to have a chimeric cell composition of the transplanted cells and the cells derived from the recipient non-human embryo. Therefore, as the recipient non-human embryo, it is desirable to use an embryo derived from an animal which has an abnormality associated with a lack of development of the organ to be produced in a development stage, and whose offspring has a deficiency of the organ. As long as the animal develops such an organ deficiency, knockout animal having an organ deficiency as a result of the deficiency of a specific gene or a transgenic animal having an organ deficiency as a result of incorporating a specific gene may be used. Alternatively, a "founder" animal described herein may be used. For example, when a kidney is produced as the organ, embryos of a Salll knockout animal having an abnormality associated with a lack of development of a kidney in the development stage (Nishinakamura, R. et al . , Development, Vol. 128, p. 3105-3115, 2001), or the like, can be used as the recipient non-human embryo. Meanwhile, when a pancreas is produced as the organ, embryos of a Pdxl knockout animal having an abnormality associated with a lack of development of a pancreas in the development stage (Offield, M. F., etal., Development, Vol. 122, p. 983-995, 1996) can be used as the recipient non-human embryo. When a cerebellum is produced as the organ, embryos of a Wnt-1 (int-1) knockout animal having an abnormality associated with a lack of development of a cerebellum in the development stage (McMahon, A. P. and Bradley, A., Cell, Vol. 62, p. 1073-1085, 1990) can be used as the recipient non-human embryo. When a lung and a thyroid gland are produced as the organ, embryos of a T/ebp knockout animal having an abnormality associated with a lack of development of a lung and a thyroid gland in the development stage (Kimura, S. , et al. , Genes and Development, Vol . 10, p. 60-69, 1996), or the like, can be used as the recipient non-human embryo. Moreover, embryos of a dominant negative-type transgenic mutant animal model (Celli, G. , et al. , EMBO J. , Vol. 17 pp. 1642-655, 1998) which overexpresses the deficiency of an intracellular domain of fibroblast growth factor (FGF) receptor (FGFR) , and which causes deficiencies of multiple organs such as kidney and lung, can be used. Alternatively, nude mice can be used for production of hair or thymus. In the present invention, the non-human animal derived from the recipient embryo may be any animal other than human, such as pig, rat, mouse, cattle, sheep, goat, horse, dog, chimpanzee, gorilla, orangutan, monkey, marmoset, and bonobo. It is preferable to collect embryos from a non-human animal having a similar adult size to that of the animal species for the organ to be produced. Meanwhile, a mammal serving as the origin of the cell that is transplanted into a recipient blastocyst stage fertilized egg and that is for formation of the organ to be produced may be either human or a mammal other than human, such as, for example, pig, rat, mouse, cattle, sheep, goat, horse, dog, chimpanzee, gorilla, orangutan, monkey, marmoset, and bonobo. The relationship between the recipient embryo and the cell to be transplanted may be an allogeanic relationship or a xenogeneic relationship. By transplanting the cell to be transplanted, prepared as described above, into the inner space of the recipient blastocyst stage fertilized egg, a chimeric cell mixture of the blastocyst-derived inner cell and the transplanted cell may be formed in the inner space of the blastocyst stage fertilized egg. The blastocyst stage fertilized egg having a cell transplanted as described above is transplanted into a womb of a surrogate parent that is a pseudo-pregnant or pregnant female animal of the species from which the blastocyst stage fertilized egg is derived. The blastocyst stage fertilized egg is developed in the womb of the surrogate parent to obtain a litter. Then, the target organ can be obtained as a mammal cell-derived target organ from this litter. Therefore, these and other advantages of the present invention will become apparent as the following detailed description is read. Advantageous Effects of Invention According to the present invention, a technique for organ regeneration is provided, the technique being suitable for industrial application. This also provides a technique for regenerating an "own organ" from a somatic cell, such a skin, depending on the circumstance of an individual. Moreover, it becomes possible to conduct research and development using organs derived from various genomes, the organs being provided by carrying out the present invention by way of producing an induced pluripotent stem cell (iPS cell) from a cell having a target genome. This can be said to be a technique which was absolutely impossible in the prior art. Furthermore, it becomes possible to avoid a part of the ethical problem that has been a problem in ES cells by use of iPS cells, and there is also an advantage that similar effects can be obtained. Brief Description of the Drawings [Fig. 1] Fig. 1 shows a therapeutic model using a construction of a pancreas derived from an iPS cell by blastocyst complementation. [Fig. 2] a. shows a strategy for establishing GFP mouse-derived iPS cells. After establishment of GFP mouse tail tip fibroblasts (TTF), three factors (reprogramming factor) were introducing into the TFT, and resulting TFT was cultured in an ES cell medium for 25 to 30 days. Then, iPS colonies were picked up, thereby establishing iPS cell lines. b. shows photographs of the morphology of thus established iPS cells taken by a microscope equipped with a camera. The left shows a photograph of GFP-iPS cell #2, and the right shows that of #3. c. shows measurements of alkaline phosphatase activity. The iPS cells were photographed under a fluorescent microscope, and subjected to staining using an alkaline phosphatase staining kit (Vector Laboratories, Inc., Cat. No. SK-5200). From the left, a bright-field image, a GFP fluorescence image, and alkaline phosphatase staining are shown. d. shows identification of the introduced three factors (reprogramming factors) by PCR on genomic DNA. It is the result obtained from PCR performed on the genomic DNA extracted from the iPS cells. From the top, expressions of Klf4, Sox2, Oct3/4, c-Myc, and Myog genes are shown. From the left, results of GFP-iPS cells #2 and #3 , Nanog-iPS (for four factors) , and ES cell (NC) as a control are shown. At the very right, a result of distilled water is shown. Insertion of the three factors in the iPS cells used in the present invention was confirmed. e. shows analysis of an ES cell-specific gene expression pattern in the cells used in the present invention and confirmation of the expression of the introduced genes, using RT-PCR. From the top, expressions of Klf4, Sox2, Oct3/4, c-Myc, Nanog, Rexl, Gapdh genes are shown. At the bottom, a negative control (RT(-)) is shown. As for Klf4, Sox2, and Oct3/4, the expressions were confirmed each for Total RNA and transgenic (Tg) . From the left, expressions of GFP-iPS cells #2 and #3 , ES cell (NC) as a control, and TTF (negative control) as another control are shown. At the very right, a result of distilled water is shown. f . shows production of a chimeric mouse using the iPS cells. A result of the production of a chimeric mouse is shown, the production being performed by injecting the established iPS cells into a blastocyst obtained from breeding C57BL6 and BDF1 mouse strains. In the upper part, a bright-field image (left) and a GFP fluorescence image (right) of the mouse on embryonic day 13.5 are shown. In the lower part, an image of the mouse in the neonatal period is shown. What denoted by NC is a negative control. [Fig. 3] Fig. 3 shows the morphologies of pancreases (5 days after birth) constructed by blastocyst complementation. While the border of the pancreas of the homo mouse is neatly made up of GFP-positive cells, that of the pancreas of the hetero mouse is chimeric, which can be observed as a dotted line. [Fig. 4 ] Fig. 4 shows histological analysis of pancreases derived from iPS cells (5 days after birth). Here; frozen section samples of pancreases derived from iPS cells were prepared, subj ected to nuclear staining with DAP I and an anti-GFP antibody and with an anti-insulin antibody, and then observed and photographed using an upright fluorescent microscope and a confocal laser microscope. From the left, bright-field images and GFP+DAPI images are shown, and staining with the anti-insulin antibody is shown on the right. The upper panels show pax1LacZ/LacZ of the present invention into which GFP-iPS cells had been introduced, and the lower panels show Pdxlwt/LacZ as a control into which GFP-iPS cells had been introduced. [Fig. 5] Fig. 5 shows an experiment for confirming the presence of cells that becomes GFP negative by silencing. Bone marrow cells were collected from the mouse shown in Fig. 3, isolating hematopoietic stem/precursor cells (c-Kit + , Sca-1+, Linage marker- :KSL cells) that were found to be GFP- by a flow cytometer, and thus isolated cells were dropped onto a 96-well plate one by one. The cells were cultured under the condition of cytokine addition for 12 days to allow formation of colonies. Genomic DNA was extracted from these colonies, and used for genotyping. This enables clonal genotyping on a single cell even if cells whose GFP expression is blocked by the gene silencing are included on the GFP- side. A host cell and a cell subjected to gene silencing can be conveniently discriminated. a. shows a strategy for a colony formation method using KSL cells isolated from bone marrow cells, b. shows the morphology of hemocyte colonies on day 12 after culture. c. shows genotyping of a chimeric individual using DNA extracted from each colony. The panels in a show, from the left, a FACS pattern of the hematopoietic stem/precursor cells, c-Kit+, Sea-1+, Linage- (KSL), in the bone marrow. Photographs in b shows , from the left, the colony on day 12 after culture, a bright-field image in the center, and a GFP fluorescence image on the left. c shows a result of genotyping performed by a PCR method on DNA extracted from a colony derived from a single cell by the above-described method using a kit of Qiagen Co. , Ltd. The PCR method was carried out using the same primers and conditions as those at the time of Pdxl litter determination. [Fig. 5A] Fig. 5A shows transplantation of iPS-derived pancreatic islets into STZ-induced diabetic mice. a and b show isolation of the pancreatic islets. The iPS-derived pancreas was perfused via the common bile duct (arrow in a.) with collagenase. After density-gradient centrifugation, iPS-derived pancreatic islets that express EGFP were concentrated (b) . c shows the kidney film two months after the transplantation of the pancreatic islets. A spot (arrow) where EGFP was expressed is the transplanted pancreatic islet. d shows HE staining (left panel) and GFP staining with DAPI (right panel) performed on a kidney section. e shows transplantation of 150 iPS-derived pancreatic islets into STZ-induced diabetic mice. Arrows indicates the time when an antibody cocktail (anti-INF-γ, anti-TNF-α, anti-IL-ß) was administered. The blood glucose level in the intraperitoneal cavity was measured every one week until two months elapsed after the transplantation. The STZ-induced diabetic mice into which the iPS-pancreatic islets were transplanted were represented by A (black triangles) (n=6), while STZ-induced diabetic mice into which no iPS-pancreatic islets were transplanted were represented by ■ (black squares). f shows a glucose tolerance test (GTT) performed two months after the transplantation of the pancreatic islets. [Fig. 6] Fig. 6 shows regeneration of kidney by Blastocyst Complementation in Sal11 knockout mice. A result from genotyping of the Salll allele is shown in the upper part. It is understood that the mouse #3 was a Salll homo KO mouse. On the lower part, the morphology of the kidney (1 day after birth) regenerated by performing blastocyst complementation using iPS cells in the mouse #3 as a host. It is understood that the whole kidney in the homo KO mouse is neatly made up of GFP-positive cells. It has been revealed that it is possible to produce a kidney derived from iPS cells using a Salll knockout mouse. [Fig. 7] Fig. 7 shows a photograph confirming that hairs grew on chimera mice born after blastocyst complementation was performed using B6-derived iPS cells. #1 is a C57BL/6(B6) wild type (control) mouse, and black hair is seen. #3 is a KSN nude mouse (control) and does not have hair. #2, 4 and 5 indicate three chimera mice thus obtained, and these individuals have hairs growing. [Fig. 8] Fig. 8 shows photographs confirming the development of thymi in chimera and control mice. The thymus is observed in the C57BL/6 (B6) wild type mouse (control) . A nude mouse does not have a thymus. Meanwhile, the thymus is observed in the chimeric mouse. [Fig. 9] Fig. 9 shows a result of analyzing GFP-positive cells obtained from CD4 - and CD8-positive cells (T cells) that were separated from peripheral blood of each of the C57BL/6 (B6) wild type (control) mouse and the chimera mice (#2 , 4, and 5) in Fig. 7. The degree of chimerism is indicated from the distributions of GFP-negative cells and GFP-positive cells. [Fig. 10] A male Pdxl {-/-) mouse (founder: which was a Pdxl (-/-) mouse having a pancreas complemented using mouse iPS cells) was bred with a female Pdxl ( + /-) mouse. Fertilized eggs were collected and developed to the blastocyst stage in vitro. The resultant blastocyst was microinjected under a microscope with 10 rat iPS cells marked with EGFP. This was transplanted into a pseudo-pregnant surrogate parent. Laparotomy was performed in the full term pregnancy. A result of analysis of neonates thus born is shown. EGFP fluorescence was observed under a fluorescent stereoscopic microscope . It was found out from the EGFP expression on the body surface that individual numbers #1, #2, and #3 were chimeras. By laparotomy, pancreases uniformly expressing EGFP were observed in #1 and #2. Meanwhile, the pancreas of #3 exhibited partial EGFP expression, however, in a mosaic manner. Although #4 was a litter-mate as #1 to 3, no EGFP fluorescence was observed on the body surface . Because the pancreas was deficient upon laparotomy, #4 was a non-chimeric Pdxl (-/-) mouse. Further, the spleens were removed from these neonates, and hemocyte cells prepared therefrom were subj ected to staining with a monoclonal antibody against mouse or rat CD45, and analyzed by a flow cytometer. As a result, in the individual numbers #1 to 3, rat CD45-positive cells were observed in addition to mouse CD45-positive cells . Thus, it was confirmed that these were xenogeneic chimeric individuals between mouse and rat containing cells derived from the host mouse and the rat iPS cells. Furthermore, almost all the cells in the rat CD45-positive cell fractions exhibited EGFP fluorescence. Thus, the rat CD45-positive cells were cells derived from the rat iPS cells marked with EGFP. [Fig. 10A] Fig. 10A shows confirmation of the Pdxl genotype by PCR of the host mouse of the individual numbers #1 to #3. In order to confirm the genotype of the host mouse, mouse CD45-positive cells, which are encompassed by dotted square lines in Fig. 10, were collected from the same spleen sample as in Fig. 1. The genomic DNA was extracted, and PCR was carried out using primers which are capable of distinguishing Pdxl mutant allele and wild type allele . As a result, in #1 and #2, only mutant bands were observed, and in the individual number #3, both bands of mutant and wild type were detected. Accordingly, it is understood that the genotype of the host is Pdxl (-/-) for #1, #2 and Pdxl (+/-) for the individual number #3. From this result, a pancreas of rat was successfully constructed in a mouse individual by applying the xenogeneic blastocyst complementation technique using the rat iPS cells as a donor in the Pdxl (-/-) mice #1 and #2 which should not originally have pancreases formed. Description of Embodiments Hereinafter, the present invention will be described. It should be understood throughout the present description that expression of a singular form includes the concept of its plurality unless otherwise mentioned. Accordingly, it should be understood that articles (for example, "a," "an, " "the, " and the like, in English) for a singular form also include the concept of their plurality unless otherwise mentioned. It should also be understood that the terms as used herein have definitions typically used in the art unless otherwise mentioned. Thus, unless otherwise defined, all technical terms and scientific terms as used herein have the same meanings as those generally understood by those skilled in the art to which the present invention pertains. If there is contradiction, the present description (inclusive of the definition) takes precedence. In order to specifically describe embodiments of the present invention, exemplary embodiments will be described hereinafter. As an example, a method for producing a kidney derived from a mammal cell in a living body of a mouse will be described hereinbelow. It is understood that a pancreas, a hair, and a thymus can also be produced by such a method. (Non-Human Animal) In order to produce a kidney derived from a cell of a mammal other than human in a living body of an animal such as a mouse, prepared is an animal such as a mouse having an abnormality associated with a lack of development of the kidney in a development stage. In one embodiment of the present invention, a Sal11 knockout mouse (Nishinakamura , R . et al . , Development, Vol . 12 8 , p . 3105-3115, 2001) can be used as the mouse having an abnormality associated with a lack of development of the kidney in a development stage. If this animal has a homozygous knockout genotype of Salll (-/-), the animal is characterized in that only the kidney does not develop, and litter individuals have no kidney. Alternatively, a founder animal described herein can also be used. This mouse has no kidney formed and cannot survive if the deficiency of Salll gene is in a homozygous state (Salll (-/-)). Thus, the deficiency of Salll gene is maintained in a heterozygous state (Salll (+/-)). Mice each in the heterozygous state are bred with each other (Salll (+/-) × Salll (+/-) ) , and fertilized eggs are collected from the womb. The fertilized eggs develop at a probability ratio of Salll (+/ + ):Salll ( + /-):Salll (-/-) = 1:2:1, in terms of probability . Int he present invention, an embryo of Salll (-/-), which develops at a probability of 25%, is used. However, it is difficult to determine the genotype in the stage of early embryo, and thus, it is practical to determine the genotype of a litter after birth and to use only individuals having the desired genotype of Salll (-/-) in the subsequent steps. This knockout mouse may have the Salll gene knocked out in the preparation stage and have a gene of a fluorescent protein for detection, or green fluorescent protein (GFP), knocked in into the Salll gene region in an expressible state (Takasato, M. et al . , Mechanisms of Development, Vol. 121, p. 547-557, 2004). When the regulatory region of this gene is activated by knocking-in such a fluorescent protein, expression of GFP occurs instead of Salll, and the deficiency state of the Sall1 gene can be determined by fluorescence detection. Further, the relationship between a recipient embryo and a cell to be transplanted in the present invention may be an allogeanic relationship or a xenogeneic relationship . There have been hitherto a large number of reports on the preparation of a chimeric animal in such a xenogeneic relationship in the art. For example, there have been actually reported about blastular chimeric animals between closely related animal species, such as the preparation of a chimera between rat and mouse (Mulnard, J. G. , C. R. Acad. Sci . Paris . 276, 379-381 (1973); Stern, M. S., Nature. 243, 472-473 (1973); Tachi, S. & Tachi, C. Dev. Biol. 80, 18-27 (1980); Zeilmarker, G., Nature, 242, 115-116 (1973)), and the preparation of a chimera between sheep and goat (Fehilly, C. B., et al . , Nature, 307, 634-636 (1984)). Therefore, in the present invention, for example, in the case of preparing a kidney derived from a cell of a mammal other than human in a living body of a mouse, a certain xenogeneic organ may be prepared in a recipient embryo based on these conventionally-known chimera creation methods (for example, a method of inserting cells to be transplanted into a recipient blastocyst (Fehilly, C. B., et al . , Nature, 307, 634-636 (1984) ) ) . The term "non-human mammal" as used herein refers to a counterpart mammal from which a chimeric animal, a chimeric embryo, or the like is produced using a cell to be transplanted. The term "different individual mammal" as used herein refers to any mammal that is an individual different from the non-human mammal, and may be an allogeanic individual orxenogeneic . The term "non-human surrogate parent mammal" as used herein refers to a mammal in which a fertilized egg formed by transplanting a cell derived from a different individual mammal that is an individual different from a non-human mammal is developed in a womb of the non-human surrogate parent mammal (serving as a surrogate parent). Note that although the terms "non-human mammal" and "non-human surrogate parent mammal" are sometimes referred to as a "non-human host mammal" or "host," the "non-human mammal" and the "non-human surrogate parent mammal" are animals different from each other. In the context of the present invention, it should be understood that which is indicated is apparent to those skilled in the art. When a pancreas is produced as the organ, embryos of a Pdxl knockout animal having an abnormality associated with a lack of development of pancreas in a development stage (Offield, M. F., et al . , Development, Vol . 122 , p. 983-995, 1996) or a founder animal described herein can be used as the recipient non-human embryo. When a hair is produced as the organ, embryos of a hairless nude mouse can be used as the recipient non-human embryo. When a thymus is produced as the organ, embryos of a nude mouse can be used as the recipient non-human embryo. (Cell to be Transplanted) Next, a cell to be transplanted into, for example, a kidney will be described. In order to produce a kidney derived from a mammal cell, an iPS cell (see Non-Patent Document 2 and so forth) or the like is prepared as the cell to be transplanted. With respect to the Salll gene, the cell has a wild type genotype (Salll (+/ + ) ) , and has an ability to develop into all kinds of cells in the kidney. This cell may incorporate a fluorescence protein for specific detection in an expressible state prior to transplantation. For example, as a fluorescent protein used for such detection, the sequence of DsRed. T4 (Bevis B. J, and Glick B. S., Nature Biotechnology Vol. 20, p. 83-87, 2002), which is a DsRed genetic mutant, may be designed so as to be expressed in organs of almost the entire body under the control of a CAG promoter (cytomegalovirus enhancer and chicken actin gene promoter), and then be incorporated into an iPS cell by electroporation. As such a fluorescence protein, one known in the art, such as a green fluorescence protein (GFP) , may be used. By performing a fluorescent labeling on such a cell for transplantation, it can be easily detected whether or not a produced organ is composed of transplanted cells only. This mouse iPS cell or the like is transplanted into the inner space of a blastocyst stage fertilized egg having the aforementioned genotype of Salll (-/-) to prepare a blastocyst stage fertilized egg having a chimeric inner cell mass. This blastocyst stage fertilized egg having a chimeric inner cell mass is developed in a womb of a surrogate parent to obtain a litter. In the case of using an iPS cell which is not marked, the cell cannot be distinguished from the embryos of the host when used in the production of chimera, and it cannot be discriminated whether the complementation of the organ has been achieved. Therefore, in order to solve the problem, a fluorescent dye can be introduced into this cell line, thereby being capable of carrying out an experiment with the same protocol as those described in Examples and the like. (Method for Producing Founder Animal for Reproduction) A founder animal for reproduction, used in the present invention, has the following characteristics: the animal includes a gene coding for a factor which causes a deficiency of any one of an organ and a body part and gives any one of no possibility of survival and difficulty in survival if the factor functions, and in which the any one of an organ and a body part is complemented by blastocyst complementation. By producing a next generation animal using this animal (also referred to as a "founder animal" herein), it is possible to cause a target organ to be deficient, and to produce an organ having a desired genome type regarding the deficient organ. Moreover, it has been revealed that production using this method enables organ production in the next generation as well, and also that the method can be used with iPS cells. Thus, there has been a big breakthrough in industrial application of the present invention. The term " any one of an organ and a body part, giving any one of no possibility of survival and difficulty in survival if the factor functions" as used herein refers to, in regard to a certain factor, one that gives any one of no possibility of survival and difficulty in survival when the factor causes the any one of an organ and a body part to be deficient or dysfunctional (for example, to be not normal) . For example, in the case of a foreign gene, when the gene is introduced into an animal and expressed normally, a deficiency occurs in a certain organ or body part, resulting in the animal being incapable of survival or having difficulty in survival. Difficulty in survival includes incapability of procreation of the next generation, and difficulty in the social life in a case of human. Such an organ or body part may be, for example, pancreas, liver, hair, thymus, or the like, but is not limited thereto. Examples of genes involved in such events include Pdx-1 (for pancreas) and the like. Incidentally, to be used for organ regeneration, a gene should be selected with which an organ can be complemented and a resulting litter does not die after birth due to other factors (being incapable of ingesting milk from a mother mouse, for example) . One example of such a gene is Pdx-1. By using a gene possessing such properties, the invention of the present application can be carried out . In addition, even with the same phenotype of, for example, pancreatic deficiency, significance largely varies. Specifically, a knockout individual has a feature of improving productivity, while a transgenic individual has a feature of enabling clonal analysis of a lethal phenotype in addition to the feature of improving productivity. The term "giving any one of no possibility of survival and difficulty in survival if the factor functions" as used herein refers to, regarding a certain factor, a condition in which, if the factor functions, an animal as a host cannot survive at all and dies, or can survive but is substantially impossible to survive later due to reasons, such as difficulties in growth and reproduction. The term can be understood by using ordinary knowledge in the art. The term "organ" as used herein is used to have an ordinary meaning in the art, and refers to organs constituting animal viscera in general. The term "body part" as used herein refers to any part of a body, and also includes ones which are not generally referred to as organs. For example, when a kidney is taken as an example, a complete kidney is created when genes are normal. However, when some gene is deficient or has an abnormality, although an organ like a kidney may be created, a part of the organ may have an abnormality or deficiency. The part having such an abnormality or deficiency can be said to be an example of this "body part." Gene defect or abnormality does not necessarily correspond to each organ, and it frequently occurs that a part thereof is affected. Accordingly, when a correspondence relationship to a gene is to be considered, it may be better to consider correspondence to a body part. Therefore, such a correspondence relationship is also taken into consideration herein. The term "blastocyst complementation" as used herein refers to a technique for complementing a defective organ or body part by using the phenomenon in which a resulting individual obtained from injection of pluripotent cells, such as ES cells and IPS cells, having multipotency into an inner space of a blastocyst stage fertilized egg forms a chimeric mouse. The inventors have discovered, regarding blastocyst complementation which had been considered to be difficult, that a mammalian organ, such as kidney, pancreas, hair, and thymus, having a complicated cellular constitution formed of multiple kinds of cells can be produced in the living body of an animal, particularly, a non-human animal. The inventors confirmed that blastocyst complementation can be carried out using iPS cells . Thus, this technique can be utilized in full scale in the present invention using iPS cells. The term "label" as used herein may be any factor as long as it is used for distinguishing a complemented organ. For example, by causing a specific gene (such as, for example, a gene for expressing a fluorescence protein) to be expressed only in an organ to be complemented, the organ to be complemented can be distinguished from a host of complementation by a property (for example, fluorescence) derived from the specific gene. As described above, it can be distinguished whether an animal became complete by complementation with cells derived from exogenous cells or an animal became complete by complementation with cells derived from endogenous cells . Thus, it is possible to select a founder animal used in the present invention more easily. These cells may incorporate a fluorescence protein for specific detection in an expressible state prior to transplantation. For example, as a fluorescent protein used for such detection, the sequence of DsRed. T4 (Bevis B. J. and Glick B. S., Nature Biotechnology Vol. 20, p. 83-87, 2002), which is a DsRed genetic mutant, may be designed so as to be expressed in organs of almost the entire body under the control of a CAG promoter (cytomegalovirus enhancer and chicken actin gene promoter), and then be incorporated into an iPS cell by electroporation. By performing a fluorescent labeling on such a cell for transplantation, it can be easily detected whether or not a produced organ is composed of transplanted cells only. Examples of such label include: green fluorescent protein (GFP) genes,* red fluorescent proteins (RFP) ; cyan fluorescent proteins (CFP); other fluorescent proteins; LacZ; and the like. A method for producing a founder animal used in the present invention includes the following steps of: A) providing a first pluripotent cell having the gene; B) growing the first pluripotent cell into a blastocyst; C) introducing a second pluripotent cell into the blastocyst so as to produce a chimeric blastocyst, the second pluripotent cell having an ability to complement a deficiency caused by the gene; and D) producing individuals from the chimeric blastocyst, and then selecting an individual in which the any one of an organ and a part thereof has been complemented by the second pluripotent cell. The terms "(deficiency responsible) gene coding for a factor which causes a deficiency of any one of an organ and a body part and gives any one of no possibility of survival and difficulty in survival if the factor functions" and "deficiency responsible gene" as used herein are used interchangeably and refers to, in regard to a certain gene, a gene that gives any one of no possibility of survival and difficulty in survival when the factor functions (for example, in the case of a foreign gene, when the gene is introduced and expressed; in the case of an intrinsic gene, when such a gene is exposed to a condition in which the gene functions; or other cases) to cause the any one of an organ and a body part to be deficient or dysfunctional (for example, to be not normal). Examples of "pluripotent cell" used herein include: an egg cell; an embryonic stem cell (ES cell) ; an induced pluripotent cell (iPS cell) ,- a multipotent germ stem cell (mGS cell); and the like. The term "first pluripotent cell" as used herein refers to a pluripotent cell used as an origin to be a host such as a founder animal (also referred to as a host herein) or to a cell mass derived therefrom. Preferably, a fertilized egg or an embryo is used. The term "second pluripotent cell" when used herein refers to a pluripotent cell used with a view of an organ to be produced, and an iPS cell is used. The term "having an ability to complement a deficiency" as used herein refers to, in regard to a factor, gene, or the like, an ability capable of complementing an organ or a body part. The term "chimeric blastocyst" as used herein refers to a blastocyst formed by a cell, which is derived from the first pluripotent cell, and a cell, which is derived from the second pluripotent cell, being in a chimeric state . Such a chimeric blastocyst can be produced by, in addition to an injection method, utilizing a method such as a so-called "agglutination method" in which embryo + embryo, or embryo + cell are closely attached to each other in a Petri dish to produce a chimeric blastocyst. Further, the relationship between a recipient embryo and a cell to be transplanted in the present invention may be an allogeanic relationship or a xenogeneic relationship. There have been hitherto a large number of reports on the preparation of a chimeric animal in such a xenogeneic relationship in the art. For example, there have been actually reported about blastular chimeric animals between closely related animal species, such as the preparation of a chimera between rat and mouse (Mulnard, J. G., C. R. Acad. Sci. Paris. 276, 379-381 (1973); Stern, M. S., Nature. 243, 472-473 (1973); Tachi , S. & Tachi , C. Dev. Biol. 80, 18-27 (1980); Zeilmarker, G., Nature, 242, 115-116 (1973)), and the preparation of a chimera between sheep and goat (Fehilly, C. B., et al., Nature, 307, 634-636 (1984)). Therefore, in the present invention, for example, in the case of preparing a kidney derived from a cell of a mammal other than human in a living body of a mouse, a certain xenogeneic organ may be prepared in a recipient embryo based on these conventionally-known chimera creation methods (for example, a method of inserting cells to be transplanted into a recipient blastocyst (Fehilly, C. B. , et al., Nature, 307, 634-636 (1984))). In the method for producing a founder animal used in the present invention, the step of providing the first pluripotent cell having the gene coding for a factor which causes a deficiency of any one of an organ and a body part and gives any one of no possibility of survival and difficulty in survival if the factor functions (the gene also refers to as the "deficiency responsible gene" herein) can be carried out, for example, by procuring a pluripotent cell having the gene, or by producing a pluripotent cell having the gene by introducing the gene into the pluripotent cell. A method of such gene introduction is well known in the art, and those skilled in the art can carry out such gene introduction by appropriately selecting a method. It is preferable to use electroporation. In electroporation, an electric pulse is applied to a cell suspension to create fine pores on a cell membrane, and DNA is sent into the cell so that transformation, that is, introduction of a target gene can be achieved. Accordingly, damage after electroporation is small. This is why electroporation is preferable, but the method is not limited thereto. In the method for producing a founder animal used in the present invention, the step of growing the first pluripotent cell (for example, a fertilized egg, an embryo, or the like) into a blastocyst can be carried out by any publicly-known method for growing a pluripotent cell into a blastocyst. The conditions for this are well known in the art, and described in Manipulating the Mouse Embryo, A LABORATORY MANUAL 3rd Edition 2002 (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York)(incorporated herein by reference). In the method for producing a founder animal used in the present invention, the step of introducing an induced pluripotent stem cell (iPS cell), which is the second pluripotent cell having an ability to complement a deficiency caused by the gene, into the blastocyst so as to produce a chimeric blastocyst may adopt any publicly-known method in the art as long as the induced pluripotent stem cell (iPS cell) as the second pluripotent cell can be introduced into the blastocyst. Examples of such a method include an injection method and agglutination; however, the method is not limited to these. In the method for producing a founder animal used in the present invention, a method for producing individuals from the chimeric blastocyst may adopt a publicly-known technique in the art. Generally, the chimeric blastocyst is returned to a surrogate parent, and then pseudo-pregnancy of the surrogate parent is caused so as to grow resulting individuals in the womb of the surrogate parent. However, the method is not limited to this technique. In the method for producing a founder animal used in the present invention, selecting of an individual in which the any one of an organ and a body part thereof complemented can be carried out by using any technique allowing confirmation of complementation of the organ or body part. An example thereof is identifying an identifier derived from the induced pluripotent stem cell (iPS cell) as the second pluripotent stem cell. The term "identifier" as used herein refers to any factor which allows specifying of a certain individual, species, or the like, and identifying of the origin thereof, and is also referred to as "ID" in its abbreviation. Such an identifier could be, for example, a genomic sequence, phenotype, or the like unique to the induced pluripotent stem cell (iPS cell) as the second pluripotent cell. Alternatively, regarding such selecting, by using the second pluripotent cell which is labeled or can be labeled (including one which can be a label by gene expression) , the selecting in the method for producing a founder mouse of the present invention may be carried out by identifying the label. In addition, it is understood that those in the art can carry out the selecting by modifying this technique as necessary. (Method of Organ Regeneration Using Founder Animal) In another aspect, the present invention provides a method for producing any one of a target organ and a target body part using a founder animal and utilizing an induced pluripotent stem cell (iPS cell). The method comprises the steps of: providing a founder animal, in which a deficiency responsible gene codes for a factor which causes a deficiency of the any one of a target organ and a target body part; B) growing an ovum obtained from the animal into an blastocyst; C) introducing an induced pluripotent stem cell (iPS cell) as a target pluripotent cell into the blastocyst so as to produce a chimeric blastocyst, the target iPS cell having a desired genome capable of complementing a deficiency caused by the gene; and D) producing an individual from the chimeric blastocyst, and then obtaining the any one of a target organ and a body part from the individual. Here, the step D) can be carried out by developing the chimeric blastocyst in a womb of a non-human surrogate parent mammal to obtain a litter, and obtaining the target organ from the litter individual. (Formation of Pancreas) The formation of a pancreas can be investigated by performing macroscopic or microscopic morphological analysis, gene expression analysis, and the like, using methods, such as visual inspection, microscopic observation after staining, and observation using fluorescence. For example, by performing visual inspection, the actual presence or absence of the organ, and features of the organ, such as the external appearance, can be investigated. Together with such a macroscopic morphological analysis, a tissue obtained after general tissue staining, such as hematoxylin-eosin staining, may be observed microscopically using a microscope. Such microscopic observation allows investigations to be performed, even on various concrete cellular compositions within the pancreas. Furthermore, the gene expression analysis using fluorescence in such a way as to emit fluorescence according to conditions may also be performed. For example, the above-described knockout mouse obtained through Pdxl-Lac-Z knock-in has the following characteristics. When a fluorescent-labeled ES cell is used in a wild type (+/ + ) or heterozygous (+/-) individual, mottled fluorescence in a chimeric state is shown even though the contribution of the ES cell is observed. On the other hand, in a homozygous (-/-) individual, uniform fluorescence is shown because the pancreas is constructed by a cell that is completely derived from the ES cell. Using such characteristics, it is possible to conveniently examine which genotype a target organ or a cell constituting the target organ has with respect to the Pdxl gene. If unmarked iPS cells are used, the cells cannot be distinguished from the embryos of the host when used in the production of chimera, and it cannot be discriminated whether the complementation of the organ has been achieved. Therefore, in order to solve this problem, a fluorescent dye can be introduced into the iPS cell line, thereby being capable of carrying out an experiment with the same protocol as above. By using the cell such as described above, it is possible to produce an organ with the same protocol as the case of using the iPS cell, and to clarify the origin. (Formation of Kidney) The formation of a kidney can be investigated by performing macroscopic or microscopic morphological analysis, gene expression analysis, and the like, using methods, such as visual inspection, microscopic observation after staining, and observation using fluorescence. For example, by performing visual inspection, the actual presence or absence of the organ, and features of the organ, such as the external appearance, can be investigated. Together with such a macroscopic morphological analysis, a tissue obtained after general tissue staining, such as hematoxylin-eosin staining, may be observed microscopically using a microscope. Such microscopic observation allows investigations to be performed, even on various concrete cellular compositions within the kidney. Furthermore, the gene expression analysis using fluorescence in such a way as to emit fluorescence according to conditions may also be performed. For example, the above-described Salll gene knockout mouse has the following characteristics. The fluorescence intensity is low when the deficiency of the Salll gene is in the homozygous state (Salll (-/-)) where GFP fluorescence occurs from both alleles, compared to the case of fluorescence when the deficiency of the Salll gene is in a heterozygous state (Salll (+/-)) where fluorescence occurs only in one allele. Using such characteristics, it is possible to conveniently examine which genotype a target organ or a cell constituting the target organ has with respect to the Sall1 gene. If unmarked iPS cells are used, the cells cannot be distinguished from the embryos of the host when used in the production of chimera, and it cannot be discriminated whether the complementation of the organ has been achieved. Therefore, in order to solve this problem, a fluorescent dye can be introduced into the iPS cell line to thereby clarify the origin. (Formation of Hair) The formation of a hair can be investigated by performing macroscopic or microscopic morphological analysis, gene expression analysis, and the like, using methods, such as visual inspection and observation using fluorescence. For example, by performing visual inspection, the actual presence or absence of a hair, and features of the hair, such as the external appearance, can be investigated. Together with such a macroscopic morphological analysis, a tissue obtained after general tissue staining, such as hematoxylin-eosin staining, may be observed microscopically using a microscope. Such microscopic observation allows investigations to be performed, even on various concrete cellular compositions within the hair. Furthermore, the gene expression analysis using fluorescence in such a way as to emit fluorescence according to conditions may also be performed. For example, in the case of the above-described nude mouse, because of strong self - fluorescence of hair, it is very-difficult to determine whether the produced hair is derived from the nude mouse or from the iPS cell with the naked eye under a fluorescent microscope. However, the observation can also be performed by means for appropriately observing the fluorescence. Using such characteristics, it is possible to conveniently examine which genotype a target organ or a cell constituting the target organ has. If unmarked iPS cells are used, the cells cannot be distinguished from the embryos of the host when used in the production of chimera, and it cannot be discriminated whether the complementation of the organ has been achieved. Therefore, in order to solve this problem, a fluorescent dye can be introduced into the iPS cell line, thereby being capable of carrying out an experiment with the same protocol as above. By using such cells as described above, it is possible to produce an organ with the same protocol as the case of using the iPS cell, and to clarify the origin. (Formation of Thymus) The formation of a thymus can be investigated by performing macroscopic or microscopic morphological analysis, gene expression analysis, and the like, using methods, such as visual inspection, microphotographs, FACS, and observation using fluorescence. For example, by performing visual inspection, the actual presence or absence of the organ, and features of the organ, such as the external appearance, can be investigated. Together with such a macroscopic morphological analysis, a tissue obtained after general tissue staining, such as hematoxylin-eosin staining, may be observed microscopically using a microscope. Such microscopic observation allows investigations to be performed, even on various concrete cellular compositions within the thymus. Furthermore, the gene expression analysis using fluorescence in such a way as to emit fluorescence according to conditions may also be performed. For example, the above-described nude mouse has the following characteristics. The nude mouse does not conventionally have thymus, but this does not affect the survival. Accordingly, the nude mouse is born naturally without the thymus and survives. If a fluorescent -labeled IPS cell is injected thereinto by blastocyst complementation, a large number of individuals in which the contribution of the iPS cell is confirmed have the thymus showing fluorescence. Using such characteristics, it is possible to conveniently examine which genotype a target organ or a cell constituting the target organ has.