WIRELESS TRANSMISSION METHOD, AND WIRELESS TRANSMITTER AND WIRELESS RECEIVER TECHNICAL HELD The present invention relates to a wireless transmission method, and a wireless transmitter and a wireless receiver, and for example, relates to a technique for use in a multiple-input and multiple-output wireless transmission technique for performing signal transmission by using a plurality of transmitting and receiving antennas in a wireless communication system such as a mobile-phone and a wireless access. BACKGROUND ART Recently, a MIMO (Multiple-Input Multiple-Output) has drawn attention as the technique for enabling a high-capacity (high-speed) data communication by effectively using a frequency band. The MIMO is the technique to transmit separate data streams from a plurality of antennas of a transmitter by using a plurality of antennas in both of the transmission and the reception, that is to say, by using the transmitter having a plurality of antennas and the receiver having a plurality of antennas, and individually separate a plurality of transmission signals (data streams) mixed on a transmission path from the signal received by each receiving antenna of the receiver by using a transmission path (channel) estimate value, thereby improving a transmission rate without requiring an enlargement of the frequency band. FIG. 8 illustrates a configuration example of the previous MIMO transmission system. The system illustrated in FIG. 8 corresponds to a system shown in FIG. 1 of the Non-Patent Document 1 to be described later, and is provided with a MIMO transmitter 100 and a MIMO receiver 200; focusing on substantial parts thereof, the MIMO transmitter 100 is provided with a user selector 101, a channel coder/modulator 102, abeam selector 103, a multibeam former 104, a scheduler 105 and a plurality of transmitting antennas 106, and the MMO receiver 200 is provided with a plurality of receiving antennas 201, a MIMO/SIMO demodulator 202, a channel decoder 203, a transmission beam measure 204 and a transmission beam/stream determiner 205. Also, in the MEVIO transmitter 100, in the user selector 101, under the control of the scheduler 105, one or more user data stream to be transferred is selected from a plurality of series of user data streams and is input to the channel coder/modulator 102, and in the channel coder/modulator 102, under the control of the scheduler 105, a required error correction coding such as a turbo coding is performed with a specified coding ratio, and after that, obtained bit series is mapped to a specified modulation scheme, for example, a symbol having a signal point (signal of the data channel) such as QPSK (Quadrature Phase Shift Keying) and 16QAM (Quadrature Amplitude Modulation) and is modulated. Meanwhile, in the channel coder/modulator 102, in addition to the data channel signal, the signal of the pilot channel (pilot symbol) used for channel estimation and the signal of the control channel (control symbol) transmitting the control information may be multiplexed. The modulated data thus-obtained is input to the beam selector 103, and in the beam selector 103, under the control of the scheduler 105, the beam used for transmitting the modulated data is selected from a plurality of fixed beams (multibeam) formed by the multibeam former 104 by just the number of streams to be transmitted and the modulated data is transmitted from the transmitting antenna 106 by the selected beam. For example, assuming that the number of transmitting antennas 106 is four and the number of fixed beams capable of being formed by the multibeam former 104 is four at the maximum, when the number of streams to be transmitted is four, all of the four beams are selected, and in a case of two streams, two beams are selected out of four beams, and in a case of one stream, one stream is selected out of four beams. On the other hand, in the MIMO receiver 200, a wireless signal transmitted from the transmitting antenna 106 of the MIMO transmitter 100 is received by each receiving antenna 201, and MIMO demodulated or SIMO (Single-Input Multi-Output) demodulated by the MIMO/SIMO demodulator 202, and the user data stream is generated. That is to say, in the MIMO/SIMO demodulator 202, the user data streams multiplexed for each of the transmitting antennas 106 are separated by a method of using an inversion matrix of a channel correlation matrix and a method of using an MLD (Maximum Likelihood Detection) algorithm, based on a channel estimate value (channel matrix) obtained by a correlation calculation of the received pilot symbol and the pilot replica, and the demodulated data is generated. The obtained demodulated data is input to the channel decoder 203, and an error correction decoding such as a turbo decoding is performed in the channel decoder 203, and decoded data of the user stream received by the data channel may be obtained. Meanwhile, each signal received at the receiving antenna 201 is also input to the' transmission beam measure 204, and a CQI (Channel Quality Indicator) value, which is an index of reception quality, is measured based on the received pilot symbol in the transmission beam measure 204, and one or more beam of which reception quality is the best is determined (selected) based on the obtained CQI value in the transmission beam/stream determiner 205. Then, information including the determined number of beams, corresponding CQI value and the beam ID is generated as feedback information to the MIMO transmitter 100 and is transmitted to the MIMO transmitter 100. The above-described feedback information is finally reported to the scheduler 105 of the MIMO transmitter 100, and thereby, the scheduler 105 controls the user selector 101, the channel coder/modulator 102 and the beam selector 103 so as to transmit the transmission user data stream as described above by the beam of the number of beams (beam ID) determined (selected) in the MIMO receiver 200 (transmission beam/stream determiner 205) and by the coding ratio and modulation scheme depending on the reported CQI value. Meanwhile, as disclosed in the Patent Document 1 to be described later, in the closed loop type MIMO transmission scheme, which performs pre-coding on the transmitting side, it is also required to send back the information of the channel matrix or the received weight (weighting coefficient of the muhibeam) obtained on the receiving side, as the feedback information to the transmitting side. Patent Document 1: Japanese Patent Application Laid-Open No. 2005-311902 Non-Patent Document 1: 3GPP TSG RAN WGI meeting #43 (Rl-051438), "Multi-beam MIMO for EUTRA Downlink", Fujitsu, November 2005 SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION For improving the transmission rate by the MIMO multiplex method, (1) a high SNR (Signal to Noise Ratio) and (2) a low interantenna correlation (or a low interbeam correlation) are required. In a case in which the condition is not satisfied, throughput characteristics by the MIMO multiplex are significantly deteriorated, so that it is advantageous to use the MIMO diversity or directional beam transmission for the sake of the throughput of the entire system. Herein, in the above-described previous technique, since the number of beams to be formed is constant irrespective of the number of transmission streams (for example, fixed to the maximum value of the number of beams capable of being formed) [in other words, a beam divergence (directional intensity) for one beam is constant], the effect by the MIMO multiplex is not obtained depending on the beam to be selected, so that the throughput characteristics may be deteriorated. For example, if the beams having a high correlation therebetween (for example, adjacent beams) are selected on the transmitting side by the feedback information from the receiving side, the separation and the demodulation processing capability of the user data streams on the receiving side are deteriorated. Therefore, if the beams having a low correlation therebetween are selected, deterioration in such a separation and demodulation processing capability may be suppressed; however, this is more deteriorated than the reception quality by the beam, which is supposed to be selected as the one of which reception quality (directional gain) is excellent for the receiving side due to the directionality of the beam. Herein, as disclosed in the Patent Document 1, although it is possible to adjust the selected interbeam correlation and the beam directionality to ease the deterioration in the separation and the demodulation processing capability and the deterioration in the reception quality by feed backing the channel matrix and the reception weight used on the receiving side as the feedback information to the transmitting side, the feedback information amount is increased and the arithmetic processing for adjustment is required. The present invention is made in view of such a problem, and an object thereof is to combine the high throughput characteristics by the low interbeam correlation and the high directional gain to obtain the excellent reception characteristic without increasing the feedback information amount in the MIMO transmission. MEANS FOR SOLVING THE PROBLEM In order to achieve the above-described object, the present invention uses a wireless transmission method, and a wireless transmitter and a wireless receiver to be described below. That is to say, (1) As a generic aspect, there provided is the wireless transmission method capable of transmitting a data stream between a wireless transmitter having a plurality of transmitting antennas and a wireless receiver having a plurality of receiving antennas by a multibeam, the method including: controlling the number of transmission beams to be formed for transmitting the data stream depending on the number of data streams to be transmitted at the wireless transmitter, and selectively receiving any one or more transmission beam from the transmission beams by the wireless receiver. (2) Herein, the wireless transmitter may control to increase the number of transmission beams in proportion as the number of transmission data streams is smaller. (3) Also, the wireless receiver may selectively receive two or more of the transmission beams having a low correlation therebetween, when the number of transmission data streams is two or larger. (4) Further, the wireless receiver may selectively receive nonadjacent transmission beams as the transmission beams having a low correlation therebetween. (5) In addition, the wireless transmitter may multiplex a pilot signal for each of the transmitting antennas to perform beam transmission by a fixed weighting coefficient, and the wireless receiver may measure a level of the transmission beam based on the pilot signal and the weighting coefficient, determine the number of transmission data streams and the transmission beam to be received based on the measured level, and report information regarding the number of transmission data streams and the transmission beam, which are determined, to the wireless transmitter, and the wireless transmitter may control the number of transmission beams based on the information reported from the wireless receiver. (6) Further, the wireless transmitter may multiplex a pilot signal for each of the transmission beams to perform beam transmission by a fixed weighting coefficient, and the wireless receiver may measure a level of the transmission beam based on the pilot signal, determine the number of transmission data streams and the transmission beam to be received based on the measured level, and report information regarding the number of transmission data streams and the transmission beam, which are determined, to the wireless transmitter, and the wireless transmitter may control the number of transmission beams based on the information reported from the wireless receiver. (7) Alternatively, the wireless transmitter may multiplex a pilot signal for each of the transmitting antennas to perform beam transmission by a variable weighting coefficient, and broadcast information regarding the weighting coefficient and information regarding the number of transmission beams to the wireless receiver, and the wireless receiver may measure a level of the transmission beam based on the pilot signal and the information regarding the weighting coefficient broadcasted from the wireless transmitter, determine the number of transmission data streams and the transmission beam to be received based on the measured level and the information regarding the number of transmission beams broadcasted from the wireless transmitter, and report information regarding the number of transmission data streams and the transmission beam, which are determined, to the wireless transmitter, and the wireless transmitter may control the number of transmission beams based on the information reported from the wireless receiver. (8) As another generic aspect, there provided is a wireless transmitter which is capable of transmitting a data stream to a wireless receiver having a plurality of receiving antennas by a multibeam, and is provided with a plurality of transmitting antennas, and number-of-transmission beams control means operable to control the number of transmission beams to be formed for transmitting the data stream depending on the number of data streams to be transmitted from the transmitting antennas. (9) Herein, the number-of-transmission beams control means may control to increase the number of transmission beams in proportion as the number of transmission data streams is smaller. (10) Also, this transmitter may be further provided with first pilot multiplex means operable to multiplex a pilot signal for each of the transmitting antennas; a first beam former operable to perform beam transmission by a fixed weighting coefficient, and first reported information receiving means to receive information regarding the number of transmission data streams and the transmission beam, determined based on a level measurement result measured for the transmission beam based on the pilot signal and the weighting coefficient in the wireless receiver and reported from the wireless receiver, wherein the number-of-transmission beams control means may control the number of transmission beams based on the information received by the first reported information receiving means. (11) Further, this transmitter may be further provided with second pilot multiplex means operable to multiplex a pilot signal for each of the transmission beams, a first beam former operable to perform beam transmission by a fixed weighting coefficient, and second reported information receiving means to receive information regarding the number of transmission data streams and the transmission beam, determined based on a level measurement result measured for the transmission beam based on the pilot signal in the wireless receiver and reported from the wireless receiver, wherein the number-of-transmission beams control means may control the number of transmission beams based on the information received by the second reported information receiving means. (12) Also, this transmitter may be further provided with first pilot multiplex means operable to multiplex a pilot signal for each of the transmitting antennas, a second beam former operable to perform beam transmission by a variable weighting coefficient, broadcasting means operable to broadcast information regarding the weighting coefficient and information regarding the number of transmission beams to the wireless receiver, and third reported information receiving means to receive information regarding the number of transmission data streams and transmission beam, determined based on a level measurement result measured for the transmission beam based on the pilot signal and the information regarding the weighting coefficient broadcasted by the broadcasting means and the information regarding the number of transmission beams broadcasted by the broadcasting means, and reported from the wireless receiver, wherein the number-of-transmission beams control means may control the number of transmission beams based on the information received by the third reported information receiving means. (13) As still another generic aspect, there provided is a wireless receiver which is capable of receiving a data stream from a wireless transmitter having a plurality of transmitting antennas by a multibeam, and is provided with a plurality of receiving antennas, and beam selective reception control means operable to selectively receive any one or more transmission beam through the receiving antennas from the transmission beams of which number of transmission beams to be formed for transmitting the data stream is controlled depending on the number of data streams to be transmitted by the wireless transmitter. (14) Herein, the beam selective reception control means may selectively receive two or more of the transmission beams having a low correlation therebetween, when the number of transmission data streams is two or larger. (15) Also, the beam selective reception control means may selectively receive nonadjacent transmission beams as the transmission beams having a low correlation therebetween. (16) Further, the wireless transmitter may multiplex a pilot signal for each of the transmitting antennas to perform beam transmission by a fixed weighting coefficient, and the beam selective reception control means may be provided with a first level measuring section to measure a level of the transmission beam based on the pilot signal and the weighting coefficient, a first determining section operable to determine the number of transmitting data streams and the transmission beam to be received based on the level measured by the first level measuring section, and a first report section to report information regarding the number of transmission data streams and the transmission beam determined by the first determining section as control information of the number of transmission beams in the wireless transmitter. (17) In addition, the wireless transmitter may multiplex a pilot signal for each of the transmitting beams to perform beam transmission by a fixed weighting coefficient, and the beam selective reception control means may be provided with a second level measuring section to measure a level of the transmission beam based on the pilot signal, a second determining section operable to determine the number of transmission data streams and the transmission beam to be received based on the level measured by the second level measuring section, and a second report section to report information regarding the number of transmission data streams and the transmission beam determined by the second determining section as control information of the number of transmission beams in the wireless transmitter. (18) Further, the wireless transmitter may multiplex a pilot signal for each of the transmitting antennas to perform beam transmission by a variable weighting coefficient, and broadcast the information regarding the weighting coefficient and the information regarding the number of transmission beam to the wireless receiver, and the beam selective reception control means may be provided with a third level measuring section to measure a level of the transmission beam based on the pilot signal and the information regarding the weighting coefficient broadcasted from the wireless transmitter, a third determining section operable to determine the number of transmission data streams and the transmission beam to be received based on the level measured by the third level measuring section and the information regarding the number of transmission beams broadcasted from the wireless transmitter, and a third report section to report information regarding the number of transmission data streams and the transmission beam determined by the third determining section as control information of the number of transmission beams in the wireless transmitter. EFFECT OF THE INVENTION According to the above-described aspects, at least any of following effect or advantage may be obtained. (1) In the transmitter, the number of transmission beams (the number of selectable beams of a transmission source) to be formed depending on the number of data streams to be transmitted is controlled (changed), so that it becomes possible to obtain good throughput characteristics (reception characteristics) without increasing the feedback information amount from the receiver to the transmitter. (2) For example, by increasing the number of transmission beams in proportion as the number of transmission data streams is smaller, the number of selectable transmission source beams increases, so that it becomes possible to obtain the high directional gain. (3) Also, in a case in which the number of transmission data streams is two or larger, by selectively receiving two or more transmission beams having a low correlation therebetween (for example, nonadjacent), it becomes possible to avoid deterioration of data stream separation capability on the receiving side and obtain high throughput characteristics due to the low interbeam correlation. BRIEF DECRIPTION OF DRAWINGS FIG. 1 is a view for illustrating an overview of an embodiment; FIG. 2 is a block diagram illustrating a configuration of a MIMO transmission system according to a first embodiment; FIG. 3 is a block diagram illustrating a configuration focusing on a transmission beam ID/stream determiner and a known selectable beam memory in FIG. 2; FIG. 4 is a flowchart for illustrating an operation (beam selection method) of the transmission beam ID/stream determiner shown in FIG. 3; FIG. 5 is a schematic diagram illustrating one example of selectable beams for illustrating an operation of the MIMO transmission system shown in FIG. 2; FIG. 6 is a block diagram illustrating a configuration of the MIMO transmission system according to a second embodiment; FIG. 7 is a block diagram illustrating a configuration of the MIMO transmission system according to a third embodiment; and FIG. 8 is a block diagram illustrating a configuration of the previous MIMO transmission system. EXPLANATIONS OF REFERENCE NUMERALS I MIMO transmitter II user selector 12 channel coder/modulator 13 beam selector 14 multibeam former 15 scheduler (beam controller) (number-of-transmission beam control means, first, second, third reported information receiving means) 16-1 to 16-n transmitting antennas 17 element pilot multiplexer (first pilot multiplex means) 17-1 to 17-n adders (multiplex circuit) 17a beam pilot multiplexer (second pilot multiplex means) 17a-l to 17a-nadders (multiplex circuits) 18 broadcast information adder (broadcasting means) 19a weight generator 19b selectable beam information generator 2 MIMO receiver 20 beam selective reception control means 21-1 to 21-M receiving antennas 22 MIMO/SIMO demodulator 23 decoder (channel decoder) 24 transmission beam measure (first, second, third level measuring section) 25 known pilot memory 26 known transmission weight memory 27 transmission beam ID/stream determiner (first, second, third determining section, first, second, third report section) 271 ranking level comparator 28 known selectable beam memory 281 comparative beam ID table 29 broadcast information extractor 30-0 to 30-9 beams BEST MODE(S) FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention is described with reference to the drawings. [A] Overview First, an overview of the embodiment to be described below is described by using FIG. 1. In FIG. 1, reference numerals 1 and 2 represent a MIMO transmitter provided with a plurality of (herein, four) transmitting antennas and a MIMO receiver provided with a plurality of receiving antennas, respectively, and it is configured such that wireless MIMO transmission is performed between the MIMO transmitter 1 and the MIMO receiver 2. The MIMO transmitter 1 is applicable, for example, as a base station device of a mobile wireless communication system, and the MIMO receiver 2 is applicable as a mobile station device (UE: User Equipment) of the system. Therefore, in a following description, the MIMO transmitter 1 is also represented as a base station device 1 or a base station 1, and the MIMO receiver 2 is also represented as a mobile station device 2 or a mobile station 2. In addition, a detailed specification conforms to a Table Al in the Non-Patent Document 1, for example. Also, in this example, the base station device 1 is configured to be able to change (control) the number of beams to be formed (beamforming) depending on the number of user data streams to be sent (transmitted) (hereinafter, also simply referred to as "transmission stream"), and the mobile station device 2 is configured to be able to selectively receive any one or more beam from a multibeam having the above-described number of beams. For example, in the base station 1, when the number of transmission streams is not large, or in the case of a single stream at the minimum, the mobile station 2 selectively receives, for example, the beam of which reception level is the maximum out of more beams formed by the base station 1. Also, as the number of transmission streams increases, a combination of selectable beams is limited. When the number of transmission streams is large, in a case of transmitting the multistream of up to the number of transmitting antennas, the beam by element transmission (also consumable that there is only one selectable number of beams) is selectively received. Meanwhile, in FIG. 1, cases in which (1) the number of transmission streams is four, (2) the number thereof is two and (3) the number thereof is one in the base station 1 are shown, respectively, and it is illustrated that in the case of (1), the base station 1 forms one beam by each of the transmitting antennas and element transmits four streams by the beam, and the mobile station 2 directly (without selecting the beam) receives the signal, which is element transmitted by one beam, in the case of (2), the base station 1 forms four beams and transmits two streams by the four beams, and the mobile station 2 selectively receives, for example, two beams having low interbeam correlation therebetween out of the four beams, and in the case of (3), the base station 1 forms eight beams and transmits one stream by the eight beams, and the mobile station 2 selectively receives one beam out of the eight beams, respectively. In this manner, it becomes possible to obtain excellent throughput characteristics and a directional gain, by making it possible to obtain the gain as large as possible at the time of one stream and by selecting the beams such that the interbeam correlation is low at the time of multistream, by changing the original number of beams selectable depending on the number of transmission streams, that is to say, the number of transmission beams to be formed (beamforming). Hereinafter, a specific example is described in detail. [B] Description of first embodiment FIG. 2 is a block diagram illustrating a configuration of the MIMO transmission system according to a first embodiment, and the MIMO transmission system shown in FIG. 2 is provided with the MIMO transmitter 1 and the MIMO receiver 2; focusing on substantial parts thereof, the MIMO transmitter 1 is provided with a user selector 11, a channel coder/modulator 12, abeam selector 13, a multibeam former 14, a scheduler (beam controller) 15, a plurality of transmitting antennas 16-1 to 16-n (n is an integer of 2 or larger) and an element pilot multiplexer 17, and the MIMO receiver 2 is provided with one or a plurality of receiving antennas 21-1 to 21-M (M is an integer of 1 or larger and possibly M=n), a MIMO/SIMO demodulator 22, a decoder (channel decoder) 23, a transmission beam measure 24, a known pilot memory 25, a known transmission weight memory 26, a transmission beam ID/stream determiner 27 and a known selectable beam memory 28. In what follows, the MIMO transmitter 1 may be referred to simply as "transmitter 1" or "transmitting side 1" and the MIMO receiver 2 may be referred to simply as "receiver 2" or "receiving side 2". Here, in the MIMO transmitter 1, the user selector 11 is operable to select one or more user data stream to be transmitted from a plurality of series of user data streams under the control of the scheduler 15, and the channel coder/modulator 12 is operable to perform a required error correction coding such as a turbo coding with a specified coding ratio under the control of the scheduler 15, and mapping obtained bit series to a specified modulation scheme, for example, a symbol having a signal point (signal of data channel) such as QPSK (Quadrature Phase Shift Keying) or 16QAM (Quadrature Amplitude Modulation), thereby modulating the same. The beam selector 13 is operable to select one or a plurality of beam used for transmitting the transmission stream (user data) coded and modulated by the channel coder/modulator 12, from a plurality of beams (multibeam) formed by the multibeam former 14, under the control of the scheduler (beam controller) 15, in greater detail, depending on feedback information (information regarding a transmission beam ID and the transmission stream) from the receiving side 2. The transmission beam ID (identification information) is uniquely defined (set) based on a transmission weight matrix W used in the multibeam former 14 to be described below (same as above). The multibeam former (first beam former) 14 is operable to form the multibeam for transmitting the transmission stream based on a predetermined transmission weight matrix (weighting coefficient) W. In this example, the transmission weight matrix W is fixed. The element pilot multiplexer (first pilot multiplex means) 17 is operable to multiplex an orthogonal pilot signal (symbol) pi for each of the transmitting antennas 16-i (i=l to n) by adders (multiplex circuits) 17-1 to 17-n of the transmitting antennas 16-1 to 16-n, respectively, and thereby, the orthogonal pilot signal pi is transmitted for each of the transmitting antennas 16-i (element). The beam controller (scheduler; number-of-transmission beam control means) 15 is operable to control the number of transmission beams formed for transmitting the transmission stream depending on the number of transmission streams by controlling beam selection in the above-described beam selector 13, and in this example, it is configured to receive the information regarding the beam ID and the number of streams determined (selected) by the transmission beam ID/stream determiner 27 on the receiving side 2 as feedback information to control the number of transmission streams and the beam (the number of transmission beams to be formed) used for transmitting the transmission stream based on the feedback information. On the other hand, in the receiver 2, the receiving antennas 21-j (j=l to M) receives the beam transmitted from each of the transmitting antennas 16-i of the transmitter 1, and the MIMO/SIMO demodulator 22 is operable to MIMO-demodulating or SIMO-demodulating the signal received by each of the receiving antennas 21-j, and the demodulated data is generated by separating the user data streams, which are multiplexed for each of the transmitting antennas 16-i, by a method of using an inversion matrix of a channel correlation matrix and a method of using an MLD algorithm, based on a channel estimate value (channel matrix) obtained by a correlation operation of the pilot signal pi and the pilot replica multiplexed on a received signal. The decoder 23 decodes the user data stream obtained by the above-described MIMO/SIMO demodulator 22 by a decoding scheme corresponding to the coding scheme in the transmitting side 1. The known pilot memory 25 stores a replica signal (pilot replica) of the pilot signal pi in advance, the known transmission weight memory 26 is for storing information of the transmission weight matrix W on the transmitting side 1 in advance, and the transmission beam measure (first level measuring section) 24 measures a level for each beam from the transmitter 1 based on the pilot replica stored in the known pilot memory 25 and the information of the transmission weight matrix W stored in the known transmission weight memory 26. The known selectable beam memory 28 stores information regarding selectable beam in advance, and in this embodiment, as shown in FIG. 3 for example, a comparative beam ID table 281 in which the number of transmission streams and a candidate beam ID are related to each other is stored. Meanwhile, in the comparative beam ID table 281 shown in FIG. 3, it is illustrated that in a case that the number of transmission streams is four, the candidate of the selectable beam (candidate beam) is one beam, ID=0, in a case that the number of transmission streams is two, the IDs of the candidate beam are 2, 4, 6, 8 (or 1, 3, 5, 7), that is to say, nonadjacent four beams of even number (or odd number) IDs, and in a case that the number of transmission streams is one, the IDs of the candidate beam are 9 beams, 1 to 9. The transmission beam ID/stream determiner (first determining section) 27 determines information regarding the transmission beam ID (the number of transmission beams) and the number of transmission streams (beam selection information) to be transmitted to the transmitter 1 as the feedback information, based on a measurement result by the transmission beam measure 24 and the information (comparative beam ID table 281) stored in the known selectable beam memory 28, and in this example, as shown in FIG. 3 for example, this is provided with a ranking level comparator 271, and by checking possibility in decreasing order of the number of transmission streams based on a measurement level (Level[ID]) of each beam (ID) measured by the transmission beam measure 24, a threshold (TH[k]) corresponding to the number of transmission streams (k) and contents of the comparative beam ID table 281, in the ranking level comparator 271, the number of transmission streams and the beam ID at that time are determined. Meanwhile, in FIG. 3, a case in which the maximum number of transmission streams is four (that is to say, k=l to 4) is shown. That is to say, the block 20 including the above-described transmission beam measure 24, the known pilot memory 25, the known transmission weight memory 26, the transmission beam ID/stream determiner 27 and the known selectable beam memory 28 functions as beam selective reception control means for selectively receiving any one or more of the transmission beams through the receiving antennas 21-j from the transmission beams of which number of transmission beams formed for transmitting the transmission stream is controlled depending on the number of transmission streams by the transmitter 1. Meanwhile, the information determined by the transmission beam ID/stream determiner 27 is fed back (reported) to the transmitter 1 through a transmission system of the receiver 2 not shown, as control information for transmission beam control (the number of beams to be formed) by the beam controller 15 in the transmitter 1. Therefore, the transmitter 1 (beam controller 15) operates according to the above-described control information (feedback information), thereby controlling the beam selector 13 and the multibeam former 14 to increase the number of transmission beams in proportion as the number of transmission streams is smaller, and controlling the beam selector 13 and the multibeam former 14 to perform the element transmission by one beam of beam E)=0 when the number of transmission streams is the maximum value. Hereinafter, an operation (beam selection method) of the MIMO transmission system of this embodiment configured as above is described in detail. First, the transmitter 1 uses a constantly uniform fixed weight as the transmission weight (matrix) W of the multibeam, and multiplexes the orthogonal pilot signal pi for each of the transmitting antennas 16-i to transmit. That is to say, in the user selector 11, under the control of the scheduler 15, one or more user data stream to be transmitted is selected from a plurality of series of user data streams and is input to the channel coder/modulator 12, and in the channel coder/modulator 12, under the control of the scheduler 15, the required error correction coding such as the turbo coding is performed with the specified coding ratio, and after that, the obtained bit series is mapped to the symbol having the signal point (signal of the data channel) such as the specified modulating scheme (QPSK or 16QAM) and is modulated. The obtained modulated data is input to the beam selector 13, and in the beam selector 13, under the control of the scheduler 15, the beam used for transmitting the modulated data is selected by the number depending on the number of streams to be transmitted from a plurality of fixed beams (multibeam) formed by the multibeam former 14, and the modulated data is transmitted from the transmitting antennas 16 by the selected beam. On this occasion, the orthogonal pilot signal pi is multiplexed by each adder 17-i of the element pilot multiplex section 17 and is transmitted from each transmitting antenna 16-i. On the other hand, in the receiver 2, the signal transmitted from the above-described transmitter 1 by the multibeam is received by each receiving antenna 21-j and is input to the MIMO/SIMO demodulator 22 and the transmission beam measure 24, respectively. In the MIMO/SIMO demodulator 22, the received signal from each receiving antenna 21-j is MIMO demodulated or SIMO demodulated to generate the user data stream. That is to say, the user data stream is separated based on the channel estimate value (channel matrix) to generate the demodulated data. An error correction decoding such as a turbo decoding is performed to the obtained demodulated data by the decoder 23, thereby, decoded data of the user data stream may be obtained. On the other hand, in the transmission beam measure 24, a level for each beam is measured based on the pilot replica in the known pilot memory 25 and the information of the known transmission weight W in the known transmission weight memory 26 (hereinafter, also referred to as a transmission weight information W). For example, when the transmission data vector, the transmission weight information (matrix), pilot vector and channel information (matrix) are represented as X=[xl, ..., xn], W=[W1, ..., Wm] (wherein, m represents the number of transmission beams), P=[pl, ..., pn] and H=[H1, ..., Hn], respectively, and the received signal on the receiving side 2 is represented as Y, Y=HP=HWX is received on the receiving side 2. Therefore, in the transmission beam measure 24, by obtaining the channel information H of each element (transmitting antenna 16-i) by using the known pilot vector P, and by obtaining HW by using the known transmission weight information W, it becomes possible to obtain the channel information of each transmission beam, so that the level measurement for each beam becomes possible based on the channel information. Then, the level measurement result (Level[ID]) for each obtained beam (ID) is input to the transmission beam ID/stream determiner 27, and by checking the possibility in the descending order of the number of the transmission streams by the ranking level comparator 271 based on the level measurement result, the threshold (TH[k]) corresponding to the number of transmission streams (k) and the contents of the comparative beam ID table 281, the number of transmission streams and the beam ID at that time are determined. That is to say, as shown in FIG. 4 for example, in a case in which the maximum number of transmission streams is four (beam ID=0), the ranking level comparator 271 first compares the level measurement result Level[ID=0] of the beam ID=0 and the threshold TH[k=4] corresponding to the number of transmission streams k=4 to check whether an equation Level[ID=0]>TH[k=4] is satisfied or not (possibility that the number of transmission streams is four) (step SI). As a result, when the equation Level[ID=0]>TH[k=4] is satisfied, the ranking level compator 271 determines that the number of transmission streams k=4 and the beam ID=0 (route Y of step 1 to step S2). On the other hand, when the equation Level[ID=0]