FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] SEQUENCE ALLOCATING METHOD, TRANSMITTING METHOD AND WIRELESS MOBILE STATION DEVICE; PANASONIC CORPORATION, A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 571-8501, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. DESCRIPTION Technical Field The present invention relates to a sequence allocating method, transmitting method and radio mobile station apparatus that are used in a cellular radio communication system. Background Art In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), a Zadoff-Chu sequence ("ZC sequence") is adopted as a reference signal ("RS") that is used in uplink. The reason for adopting a ZC sequence as an RS is that a ZC sequence has a uniform frequency characteristic and has good auto-correlation and cross-correlation characteristics. A ZC sequence is a kind of CAZAC (Constant Amplitude and Zero Auto-correlation Code) sequence and represented by following equation 1 or equation 2. [1] In equation 1 and equation 2, "N" is the sequence length, "r" is the ZC sequence number, and "N" and "r" are coprime. Also, "q" is an arbitrary integer. It is possible to generate N-l quasi-orthogonal sequences of good cross-correlation characteristics from a ZC sequence having the sequence length N of a prime number. In this case, the cross-correlation is constant at √N between the N-l quasi-orthogonal sequences generated. Here, in the RS's that are used in uplink, the reference signal for channel estimation used to demodulate data (i.e. DM-RS (Demodulation Reference Signal)) is transmitted in the same band as the data transmission bandwidth. That is, when the data transmission bandwidth is narrow, a DM-RS is also transmitted in a narrow band. For example, if the data transmission bandwidth is one RB (Resource Block), the DM-RS transmission bandwidth is also one RB. Likewise, if the data transmission bandwidth is two RB's, the DM-RS transmission bandwidth is also two RB's. Also, in 3GPP LTE, one RB is comprised of twelve subcarriers. Consequently, a ZC sequence having a sequence length N of 11 or 13 is used as a DM-RS that is transmitted in one RB, and a ZC sequence having a sequence length N of 23 or 29 is used as a DM-RS that is transmitted in two RB's. Here, when a ZC sequence having a sequence length N of 11 or 23 is used, a DM-RS of 12 subcarriers or 24 subcarriers is generated by cyclically expanding the sequence, that is, by copying the head data of the sequence to the tail end of the sequence. On the other hand, when a ZC sequence having a sequence length N of 13 or 29 is used, a DM-RS of 12 subcarriers or 24 subcarriers is generated by performing truncation, that is, by deleting part of the sequence. As a method of allocating ZC sequences, to reduce the interference between DM-RS's that are used between different cells, that is, to reduce the inter-cell interference of DM-RS, in each RB, ZC sequences of different sequence numbers are allocated to adjacent cells as DM-RS's. The data transmission bandwidth is determined by the scheduling in each cell, and therefore DM-RS's of different transmission bandwidths are multiplexed between cells. However, if ZC sequences of different transmission bandwidths, that is, ZC sequences of different sequence lengths, are multiplexed, a specific combination of ZC sequence numbers has a high cross-correlation. FIG.l is a diagram illustrating cross-correlation characteristics between ZC sequences in combinations of different sequence numbers, which are acquired by computer simulation,. To be more specific, FIG.l illustrates the cross-correlation characteristics between a ZC sequence of a sequence length N=11 and sequence number r=3, and ZC sequences of a sequence length N=23 and sequence numbers r=l to 6. In FIG.l, the horizontal axis represents the delay time using the number of symbols, and the vertical axis represents the normalized cross-correlation values, that is, the values dividing the cross-correlation values by N. As shown in FIG.l, the maximum cross-correlation value is very high with the combination of a ZC sequence of r=3 and N = l 1 and a ZC sequence of r=6 , and N=23, and is about three times higher than the cross-correlation value in the single transmission bandwidth, 1/√N, that is, 1/√l 1. FIG.2 is a diagram illustrating the inter-cell interference of DM-RS in a case where specific combinations of ZC sequences that increase cross-correlation are allocated to adjacent cells. To be more specific, a ZC sequence of r=a and N=ll and a ZC sequence of r=b and N=23 are allocated to cell #A, and a ZC sequence of r=c and N=23 and a ZC sequence of r=d and N=ll are allocated to cell #B. In this case, the combination of the ZC sequence of r=a and N=ll allocated to cell #A and the ZC sequence of r=c and N=23 allocated to cell #B, or the combination of the ZC sequence of r=b and N=23 allocated to cell #A and the ZC sequence of r=d and N=ll allocated to cell #B, increases the inter-cell interference of DM-RS, and, consequently, degrades the accuracy of channel estimation and degrades the data demodulation performance degrades significantly. To avoid such problems, the ZC sequence allocating method disclosed in Non-Patent Document 1 is used in a cellular radio communication system. To reduce inter-cell interference, Non-Patent Document 1 suggests allocating a combination of ZC sequences of high cross-correlation and different sequence lengths, to a single cell. FIG.3 is a diagram illustrating the ZC sequence allocating methods disclosed in Non-Patent Document 1 and Non-Patent Document 2. In FIG.3, the example shown in FIG.2 is used. As shown in FIG.3, a combination of ZC sequences of high cross-correlation, that is, a combination of a ZC sequence of r=a and N=l 1 and a ZC sequence of r=c and N=23, is allocated to a single cell (cell #A in this case). Also, another combination of ZC sequences of high cross-correlation, that is, a combination of a ZC sequence of r=d and N=l 1 and a ZC sequence of r=b and N=23, is allocated to a single cell (cell #B in this case). In the single cell, transmission bands are scheduled by one radio base station apparatus, and, consequently, ZC sequences of high correlation allocated to the same cell, are not multiplexed. Therefore, inter-cell interference is reduced. Also, Non-Patent Document 2 proposes a method of finding a combination of ZC sequence numbers, which are used in RB's (hereinafter referred to as a "sequence group"). ZC sequences have a feature of having higher cross-correlation when the difference of r/N, that is, the difference of sequence number / sequence length is smaller. Therefore, based on a sequence of an arbitrary RB (e.g. one RB), ZC sequences that make the difference of r/N equal to or less than a predetermined threshold, are found from the ZC sequences of each RB, and the multiple ZC sequences found are allocated to a cell as one sequence group. FIG.4 is a diagram illustrating a sequence group generation method disclosed in Non-Patent Document 2. In FIG.4, the horizontal axis represents r/N, and the vertical axis represents the ZC sequence of each RB. First, the reference sequence length Nb and reference sequence number rb are set. Hereinafter, a ZC sequence having the reference sequence length Nb and reference sequence number rb is referred to as a "reference sequence." For example, if Nb is 13 (which is the sequence length associated with one RB) and rb is 1 (which is selected between 1 and Nb-1), rb/Nb is 1/13. Next, ZC sequences that make the difference of r/N from the reference rb/Nb equal to or less than a predetermined threshold, are found from the ZC sequences of each RB to generate a sequence group. Also, the reference sequence number is changed, and, in the same process as above, other sequence groups are generated. Thus, it is possible to generate different sequence groups for the number of reference sequence numbers, that is, it is possible to generate Nb-1 different sequence groups. Here, if ranges for selecting ZC sequences, in which a difference from rb/Nb is equal to or less than a predetermined threshold, overlap between adjacent sequence groups, the same ZC sequences are included in the plurality of sequence groups, and therefore the sequence numbers overlap between cells. Therefore, to prevent ranges for selecting ZC sequences in adjacent sequence groups from overlapping, the above predetermined threshold is set to, for example, a value less than l/(2Nb). FIG.5A and FIG.5B illustrate examples of sequence groups generated by the sequence group generation method disclosed in Non-Patent Document 2. Here, the sequence length N is set to the prime number that is larger than the maximum possible size of transmission in the transmission bandwidth and that is the closest to this size, and, furthermore, the sequence length N is uniquely determined from the number of RB's. FIG.5A and FIG.5B illustrate sequence groups (ZC sequence group 1 and ZC sequence group 2) comprised of ZC sequences that satisfy following equation 3 in a case where the reference sequence - length Nb is 13 and the reference sequence number rb is 1 or 2. In equation 3, the threshold Xth is, for example, l/(2Nb), (i.e. 1/26) to prevent the same sequence from being included in a plurality of sequence groups. Thus, according to the sequence allocating methods disclosed in Non-Patent Document 1 and Non-Patent Document 2, a sequence group comprised of ZC sequences that make a difference of r/N equal to or less than a predetermined threshold, that is, a sequence group comprised of ZC sequences having greater cross-correlation than a predetermined threshold, is generated, and the generated sequence group is allocated to the single cell. By this means, it is possible to allocate a combination of ZC sequences of large cross-correlation and different sequence lengths to the single cell, and reduce inter-cell interference. Non-Patent Document I: Huawei , Rl-070367, "Sequence Allocating method for E-UTRA Uplink Reference Signal", 3GPP TSG RAN WGlMeeting #47bis, Sorrento, Italy 15 -19 January, 2007 Non-Patent Document 2: LG Electronics, Rl-0?1542, "Binding method for UL RS sequence with different lengths", 3GPP TSG RAN WGlMeeting #48bis, St. Julians, Malta, March 26 - 30, 2007 Disclosure of Invention Problems to be Solved by the Invention However, with the sequence allocating method disclosed in Non-Patent Document 2, the threshold Xth related to a difference of r/N is a fixed value regardless of the number of RB's, and, consequently, the following problem arises. FIG.6 is a diagram illustrating a problem that arises when the threshold Xth is set higher. As shown in FIG.6, if the threshold Xth is set higher, ZC sequences located near the boundary of adjacent sequence groups have a smaller difference of r/N, and therefore cross-correlation increases. That is, the cross-correlation between sequence groups increases. FIG.7A and FIG.7B illustrate problems that arise when the threshold Xth is set higher, using specific examples of sequence groups. In FIG-7A and FIG.7B, the sequence group examples shown in FIG.5A and , FIG.5B are used, In the ZC sequences included in the two sequence groups (i.e. ZC sequence group 1 and ZC sequence group 2) shown in FIG 7A and FIG.7B, the hatched ZC sequences have a smaller difference of r/N from and larger cross-correlation with ZC sequences of other sequence groups. Here, as shown in FIG.4, the number of ZC sequences in each RB is N-l at 1/N intervals in the range of r/N=0 to 1. Therefore, as shown in FIG.7A and FIG.7B, when the number of RB's is larger, the number of ZC sequences increases that make a difference of r/N from a reference ZC sequence smaller than a threshold. Also, when the number of RB's is larger, that is, when the sequence length N is longer, the number of hatched ZC sequences increases. By contrast, when the threshold Xth is set smaller, the number of ZC sequences forming a sequence group decreases. Especially, when the number of RB's is smaller, that is, when the sequence length N is shorter, the number of sequences that are present in the range of r/N=0 to 1 at 1/N intervals, N-l, decreases, and, consequently, when the threshold is further smaller, the number of ZC sequences forming a sequence group further decreases. Also, to randomize the influence of interference, if sequence hopping to switch sequence numbers at predetermined time intervals is adapted and there are few candidates of sequence numbers to be switched, the randomization of interference provides no effect. It is therefore an object of the present invention to provide a sequence allocating method that can reduce cross-correlation between different sequence groups while maintaining the number of ZC sequences forming a sequence group that are allocated, in a cellular radio communication system. Means for Solving the Problem The sequence allocating method of the present invention for Zadoff-Chu sequences represented by equation 1 in a cellular radio communication system, includes: a reference setting step of setting a reference sequence length Nb and a reference sequence number rb; a first threshold setting step of setting a first threshold based on the sequence length N; a selecting step of selecting a plurality of Zadoff-Chu sequences, in which a first difference representing a difference between rb/Nb and r/N is equal to or less than the first threshold, from the Zadoff-Chu sequences generated according to the equation 1; and an allocating step of allocating the plurality of Zadoff-Chu sequences selected, to a same cell. The radio mobile station of the present invention that transmits Zadoff-Chu sequences represented by equation 1 as a reference signal, employs a configuration having: a setting section that sets a threshold based on a sequence length N signaled from a radio base station apparatus; a selecting section that selects a Zadoff-Chu sequence, in which a difference between rb/Nb and r/N is equal to or less than the threshold, from the Zadoff-Chu sequences generated according to equation 1, using a reference sequence number rb and a reference sequence length Nb signaled from the radio base station apparatus; and a transmitting section that transmits the selected Zadoff-Chu sequence as the reference signal. The transmitting method of the present invention whereby a radio mobile station apparatus transmits Zadoff-Chu sequences represented by equation I as a reference signal, in which the radio mobile station apparatus receives a sequence length N and a reference sequence number rb signaled from the radio base station apparatus; selects a Zadoff-Chu sequence, which satisfies a condition that a difference between rb/Nb (where Nb is a reference sequence length) and r/N is equal to or less than a threshold associated with the sequence length N, using the received sequence length N and the received reference sequence number rb; and transmits the selected Zadoff-Chu sequence as the reference signal. Advantageous Effect of Invention According to the present invention, it is possible to reduce cross-correlation between different groups while maintaining the number of ZC sequences forming sequence groups. Brief Description of Drawings FIG.l is a diagram illustrating cross-correlation characteristics between ZC sequences in combinations of different sequence numbers, which are acquired by computer simulation, according to the prior art; FIG.2 is a diagram illustrating inter-cell interference between DM-RS's in a case where specific combinations of ZC sequences that increase cross-correlation are allocated to adjacent cells, according to the prior art; FIG.3 is a diagram illustrating a method of allocating ZC sequences according to the prior art; FIG.4 is a diagram illustrating a method of generating sequence groups according to the prior art; FIG.5A is a diagram illustrating an example of a sequence group generated by a sequence group generation method according to the prior art (ZC sequence group 1); FIG.5B is a diagram illustrating an example of a sequence group generated by a sequence group generation method according to the prior art (ZC sequence group 2); FIG.6 is a diagram illustrating a problem with the prior art that arises when the threshold Xth is set higher; FIG.7A is a diagram illustrating a problem with the prior art that arises when the threshold Xth is set higher, using a detailed example of a sequence group (ZC sequence group 1); FIG.7B is a diagram illustrating a problem with the prior art that arises when the threshold Xth is set higher, using a detailed example of a sequence group (ZC sequence group 2); FIG.8 is a flowchart showing the process of a sequence allocating method in a cellular radio communication system, according to Embodiment 1 of the present invention; FIG.9 is a diagram illustrating a method of setting a threshold in a sequence allocating method according to Embodiment 1 of the present invention; FIG.10A is a diagram illustrating an example of a sequence group acquired by a sequence allocating method according to Embodiment 1 of the present invention (ZC sequence group 1); FIG.10B is a diagram illustrating an example of a sequence group acquired by a sequence allocating method according to Embodiment 1 of the present invention (ZC sequence group 2); FIG.11 is a diagram illustrating a method of setting a threshold according to a sequence allocating method according to Embodiment 1 of the present invention; FIG.12A is a diagram illustrating an example of a sequence group acquired by a sequence allocating method according to Embodiment 1 of the present invention (ZC sequence group 1); FIG.12B is a diagram illustrating an example of a sequence group acquired by a sequence allocating method according to Embodiment 1 of the present invention (ZC sequence group 2); FIG.13 is a block diagram showing the configuration of a radio base station apparatus to which a sequence group is allocated, according to Embodiment 1 of the present invention; FIG.14 is a block diagram showing the configuration inside a ZC sequence setting section according to Embodiment 1 of the present invention; FIG.15 is a block diagram showing the configuration of a radio mobile station apparatus according to Embodiment 1 of the present invention; FIG.16 is a diagram illustrating the cross-correlation characteristic ascertained by computer simulation according to Embodiment 2 of the present invention; FIG.17 is a flowchart showing the process of a sequence allocating method in a cellular radio communication system according to Embodiment 2 of the present invention; FIG.18 is a diagram illustrating a method of generating sequence groups based on the process of a sequence allocating method according to Embodiment 2 of the present invention; FIG.19A is a diagram illustrating an example of a sequence group acquired by a sequence allocating method according to Embodiment 2 of the present invention (ZC sequence group 1); FIG.19B is a diagram illustrating an example of a sequence group acquired by a sequence allocating method according to Embodiment 2 of the present invention (ZC sequence group 8); FIG.20A is a diagram illustrating an example of a sequence group acquired when the number of RB's allowing sequences to be deleted, is set 10 or greater (ZC sequence group 1); and FIG.20B is a diagram illustrating an example of a sequence group acquired when the number of RB's allowing sequences to be deleted, is set 10 or greater (ZC sequence group 8). Best Mode for Carrying Out Invention Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. Here, in these embodiments, components providing the same functions will be assigned the same reference numerals and overlapping explanations will be omitted. (Embodiment 1) FIG.8 is a flowchart showing the process of a sequence allocating method in a cellular radio communication system according to Embodiment 1 of the present invention. First, in step (hereinafter "ST") 101, the reference sequence length Nb and the reference sequence number rb are set for a generated sequence group. Here, the sequence number rb corresponds to the sequence group number and is lower than Nb. In ST 102, the number of RB's, m, is initialized to 1. In ST 103, the threshold Xth(m) associated with the number of RB's m is set. Here, the method of setting the threshold Xth(m) will be described later. IN ST 104, the ZC sequence length N associated with the number of RB's m is set. The number of RB's "m" and the sequence length N are uniquely associated. For example, N is a prime number that is larger than the maximum possible size of transmission with the number of RB's, m, and that is the closest to this size. In ST 105, the sequence number r is initialized to 1. In ST 106, whether or not r and N satisfy following equation 4 is decided. |r/N-rb/Nb| FIG.9 is a diagram illustrating threshold Xth(m) setting method 1 in a sequence allocating method according to the present embodiment. As shown in FIG.9, the threshold Xth(m) is set smaller when an RB is greater. For example, as shown in following equation 6, the Xth(m) is set to decrease by a predetermined value every time the number of RB's m increases. Xth(m)=l/(2Nb)-(m-l)x0.0012 ...(Equation 6) By setting the threshold Xth(m) in this way, ZC sequences located near the boundary of adjacent sequence groups have a greater difference of r/N, so that it is possible to suppress an increase of cross-correlation. Also, by increasing the threshold Xth(m) associated with a smaller number of RB's, it is possible to increase the number of ZC sequences and maintain it above a predetermined number. FIG.10A and FIG.10B illustrate examples of sequence groups acquired by the sequence allocating methods shown in FIG.8 and FIG.9. To be more specific, the sequence groups shown in FIG.10A and FIG.10B are acquired according to the following conditions and process. For example, to generate ZC sequence group 1 shown in FIG.10A, in ST 101, Nb=13 and rb=l are set. Here, Nb=13 represents the sequence length associated with the number of RB's m=l, and the sequence number rb=l corresponds to the sequence group number. Next, in the process of ST 102, the threshold Xth(m) associated with the number of RB's is set using above equation 6, and, in the process of ST 104 to ST 107, the sequence number r that makes the difference between rb/Nb and r/N equal to or less than the threshold Xth(m) is selected, to generate ZC sequence group 1. The conditions and process for generating ZC sequence group 2 shown in FIG.1OB differ from those in the case of ZC sequence group 1, only in setting the reference sequence number rb to 2 in ST 101. FIG.11 is a diagram illustrating threshold Xth(m) setting method 2 in a sequence allocating method according to the present embodiment. As shown in FIG.11, a threshold for the number of RB's "m" is set, and threshold Xth(m) is set higher below the threshold for the number of RB's than above the threshold for the number of RB's. For example, as shown in following equation 7, the threshold for the number of RB's m is 10, and, if the number of RB's m is equal to or lower than 10, Xth(m) is set to 1/2 Nb, and, if the number of RB's m is higher than 10, Xth(m) is set to 1/4 Nb. That is, the threshold Xth(m) is switched between two fixed values across the sequence length N associated with the number of RB's of 10, and the fixed value associated with the sequence lengths N's associated with the numbers of RB's equal to or less than 10 is set lower than the fixed value associated with the sequence lengths N's associated with the numbers of RB's greater than 10. Xth(m)=l/(2Nb) (in the case of lll) ...(Equation 7) By setting the threshold Xth(m) in this way, ZC sequences located near the boundary of adjacent sequence groups have a grater difference of r/N, so that it is possible to suppress an increase of cross-correlation. Also, by increasing the threshold Xth(m) associated with the numbers of RB's lower than the threshold for the number of RB's m, it is possible to increase the number of ZC sequences and maintain it above a predetermined number. FIG.12A and FIG.12B illustrate examples of sequence groups acquired by the sequence allocating methods shown in FIG.8 and FIG. 11. To be more specific, the conditions and process for acquiring the sequence groups shown in FIG.12A and FIG.12B (i.e. ZC sequence group 1 and ZC sequence group 2) differ from the conditions and process for acquiring the sequence groups shown in FIG.10A and FIG.10B (i.e. ZC sequence group 1 and ZC sequence group 2), only in using equation 7, instead of equation 6, for the method of setting the threshold Xth(m). Next, the operations of a radio base station apparatus that is present in a cell, to which sequence groups generated based on the sequence allocating method according to the present embodiment are allocated, will be explained. FIG.13 is a block diagram showing the configuration of radio base station apparatus 100, to which sequence groups are allocated, according to the present embodiment. Encoding section 101 encodes transmission data and control signal for a radio mobile station apparatus that is present in the same cell as that of radio base station apparatus 100, and outputs the encoded data to modulating section 102. Here, the control signal includes the reference sequence length Nb and the reference sequence number rb associated with the sequence group number, and the reference sequence length Nb and the reference sequence number rb are transmitted to, for example, radio mobile station apparatus 200, which will be described later, via a broadcast channel. The control signal also includes scheduling information showing the transmission bandwidth including, for example, the number of RB's for transmission allocated to radio mobile station 200 and the sequence length N, and this scheduling information is transmitted to radio mobile station apparatus 200 via a control channel. Modulating section 102 modulates the encoded data received as input from encoding section 101 and outputs the modulated signal to RF (Radio Frequency) transmitting section 103. RF transmitting section 103 performs transmission processing such as A/D conversion, up-conversion and amplification on the modulated signal received as input from modulating section 102, and transmits the signal subjected to transmission processing via antenna 104. RF receiving section 105 performs reception processing such as down-conversion and A/D conversion on a signal received via antenna 104, and outputs the signal subjected to reception processing to demultiplexing section 106. Demultiplexing section 106 demultiplexes the signal received as input from RF receiving section 105 into a reference signal, data signal and control signal, outputs the reference signal to DFT (Discrete Fourier Transform) section 107 and outputs the data signal and control signal to DFT section 114. DFT section 107 transforms the time domain reference signal received as input from demultiplexing section 106 into a frequency domain signal by performing DFT processing, and outputs the transformed, frequency domain reference signal to demapping section 109 in channel estimating section 108. Channel estimating section 108 is provided with demapping section 109, dividing section 110, IFFT section 111, mask processing section 112 and DFT section 113, and estimates the channel based on the reference signal received as input from DFT section 107. Demapping section 109 extracts, from the frequency band reference signal received as input from DFT section 107, a ZC sequence corresponding to the transmission band of each radio mobile station apparatus 200, and outputs the extracted ZC sequences to dividing section 110. ZC sequence setting section 1000 calculates the ZC sequences used in radio mobile station apparatuses 200, based on the reference sequence length Nb, the reference sequence number rb and the number of RB's assigned to each radio mobile station apparatus 200, which are included in control information received as input, and outputs the results to dividing section 110. Here, the internal configuration and operations of ZC sequence setting section 1000 will be described later. Dividing section 110 divides the ZC sequences corresponding to each radio mobile station apparatus 200, calculated in ZC sequence setting section 1000, by the ZC sequences actually used in each radio mobile station apparatus 200 and received as input from demapping section 109, and outputs the division result to IFFT (Inverse Fast Fourier Transform) section 111. IFFT section 111 performs IFFT processing on the division result received as input from dividing section 110, and outputs the signal subjected to IFFT processing to mask processing section 112. Mask processing section 112 extracts the correlation value in the region in which the correlation value of the desired cyclic shift sequence is present, that is, extracts the correlation value in the window part, by performing mask processing on the signal received as input from IFFT section 111, and outputs the extracted correlation value to DFT section 113. DFT section 113 performs DFT processing on the correlation value received as input from mask processing section 112, and outputs the correlation value subjected to DFT processing to frequency domain equalization section 116. Here, the signal subjected to DFT processing outputted from DFT section 113, represents the frequency response of the channel. DFT section 114 transforms the time domain data signal and control signal received as input from demultiplexing section 106, into the frequency domain by performing DFT processing, and outputs the transformed, frequency domain data signal and control signal to demapping section 115. Demapping section 115 extracts the data signal and control signal corresponding to the transmission band of each radio mobile station apparatus 200, from signals received as input from DFT section 114, and outputs the extracted signals to frequency domain equalization section 116. Frequency domain equalization section 116 performs equalization processing on the data signal and control signal received as input from demapping section 115, using a signal which is received as input from DFT section 113 in channel estimating section 108 and which represents the frequency response of the channel, and outputs the signals subjected to equalization processing to IFFT section 117. IFFT section 117 performs IFFT processing on the data signal and control signal received as input from frequency domain equalization section 116, and outputs the signals subjected to IFFT processing to demodulating section 118. Demodulating section 118 performs demodulation processing on the signals subjected to IFFT processing received as input from IFFT section 117, and outputs the signals subjected to demodulation processing to decoding section 119. Decoding section 119 performs decoding processing on the signals subjected to demodulation processing received as input from demodulating section 118, and extracts received data. FIG. 14 is a block diagram showing the configuration inside ZC sequence setting section 1000. Threshold calculating section 1001 calculate the threshold Xth(m) according to above equation 6 or equation 7, using the number of RB's m included in control information received as input, and outputs the result to sequence number calculating section 1002. Sequence number calculating section 1002 calculates the sequence length N of a ZC sequence that can be used as a reference signal, based on the number of RB's m included in control information received as input, and outputs the result to ZC sequence generating section 1004. Also, sequence number calculating section 1002 calculates the sequence number r of a ZC sequence that can be used as a reference signal, based on the calculated sequence length N, the reference sequence number rb and the reference sequence length Nb included in the control information received as input, and the threshold Xth(m) received as input from threshold calculating section 1001, and outputs the result to parameter determining section 1003. Parameter determining section 1003 selects one of usable r's received as input from sequence number calculating section 1002, and outputs the result to ZC sequence generating section 1004. To be more specific, parameter determining section 1003 selects r corresponding to the remainder acquired by dividing the frame number or slot number by the number of usable r's, that is, corresponding to the result of performing a modulo operation of the frame number or slot number by the number of usable r's. For example, upon receiving as input four usable r's of r=a, b, c and d from sequence number calculating section 1002, parameter determining section 1003 selects r=a when a result of performing a modulo operation on the frame number or slot number by 4 is 0, selects r=b when the result is 1, selects r=c when the result is 2, and selects r=d when the result is 3. By this means, it is possible to realize sequence hopping. ZC sequence generating section 1004 generates a ZC sequence according to equation 1 or equation 2, using "r" received as input from parameter determining section 1003 and "N" received as input from sequence number calculating section 1002, and outputs the result to dividing section 110. As described above, radio base station apparatus 100 signals the reference sequence number rb, the reference sequence length Nb and the number of RB's, to radio mobile station apparatus 200. Next, radio mobile station apparatus 200 that generates a ZC sequence used as a reference signal will be explained, using the reference sequence number rb, the reference sequence length Nb and the number of RB's signaled from radio base station apparatus 100. FIG.15 is a block diagram showing the configuration of radio mobile station apparatus 200 according to the present embodiment. Here, in FIG.15, the receiving system of radio mobile station apparatus 200 will be omitted, and the transmitting system alone will be shown. In FIG.15, similar to ZC sequence setting section 1000 provided in radio base station apparatus 100, ZC sequence setting section 1000 provided in radio mobile station apparatus 200 calculates a ZC sequence based on the reference sequence number rb, the reference sequence length Nb and the number of RB's m included in control information transmitted from radio base station apparatus 100, and outputs the result to mapping section 201. Mapping section 201 maps the ZC sequence received as input from ZC sequence setting section 1000, to the transmission band of radio mobile station apparatus 200, and outputs the mapped ZC sequence to IFFT section 202. IFFT section 202 performs IFFT processing on the ZC sequence received as input from mapping section 201, and outputs the ZC sequence subjected to IFFT processing to RF transmitting section 203. RF transmitting section 203 performs transmission processing such as D/A conversion, up-conversion and amplification on the ZC sequence received as input from IFFT section 202, and transmits the signal subjected to transmission processing, via antenna 204. Thus, according to the present embodiment, when the number of RB's increases, that is, when the ZC sequence length N is longer, a sequence group is generated using sequences that make the difference between r/N and rb/Nb smaller, and allocated to the single cell. By this means, it is possible to maintain a predetermined number of sequences in each RB while reducing cross-correlation between different sequence groups, thereby reducing inter-cell interference. Also, although an example case has been described above with the present embodiment where the sequence length of one RB is used as the reference sequence length Nb in ST 101, the present invention is not limited to this, and it is equally possible to set the reference sequence length Nb adaptively. For example, taking into account that, amongst ZC sequences forming a certain sequence group, the reference ZC sequence has the lowest cross-correlation with other sequence groups, the reference sequence length Nb is the sequence length associated with the number of RB's used in a radio mobile station apparatus in the cell edge of the poorest received quality. By this means, it is further possible to reduce inter-cell interference. Also, in a cellular communication system, it is equally possible to set the reference sequence length Nb based on the number of sequence groups required to reduce inter-cell interference. For example, when the number of sequence groups required is 100, the sequence length that is the closest to 100, that is, a sequence length of 109, associated with nine RB's, is set as the reference sequence length Nb. It is possible to generate 108 ZC sequences from nine RB's, that is, from a sequence length of 109, so that it is possible to select 100 reference sequence number r's from 108 reference sequence number r's and generate 100 different sequence groups. Also, an example case has been described above with the present embodiment where the number of ZC sequences associated with a larger number of RB's is limited by setting the threshold Xth(m) smaller when the number of RB's is larger. However, the present invention is not limited to this, and it is equally possible to find predetermined ZC sequences arranged in ascending order of the difference between r/N and rb/Nb, and form a sequence group. That is, ZC sequences that make the difference between r/N and rb/Nb smaller are preferentially selected until the number of ZC sequences reaches a predetermined number. If the sequences are arranged based on the magnitude of r/N, the interval between sequences is 1/N, and the interval between sequences is smaller when an RB is larger (i.e. N is larger). Therefore, by the process of limiting the number of sequences, it is possible to provide the same effect as provided in the process of making the threshold Xth (m) smaller when an RB is larger. That is, even if sequence groups are generated in the above way, it is equally possible to provide an effect of reducing cross-correlation between sequence groups. Also, an example case has been described above with the present embodiment where the reference sequence length Nb signaled from radio base station apparatus 100 to radio mobile station apparatus 200, with an assumption that the reference sequence length Nb varies between cells. However, the present invention is not limited to this, and, if a reference sequence length Nb that is common between all cells is determined in advance, signaling is not necessary. Alternatively, it is equally possible to determine in advance the reference number of RB's instead of the reference sequence length Nb. The numbers of RB's and sequence lengths are uniquely associated, so that it is possible to derive the reference sequence length Nb from the reference number of RB's. Also, an example case has been described above with the present embodiment where sequence number calculating section 1002 calculates the usable sequence number r using the reference sequence number rb, the reference sequence length Nb and the number of RB's m. However, the present invention is not limited to this, and, if radio base station apparatus 100 and radio mobile station apparatus 200 hold the sequence groups shown in FIG.10A and FIG.10B or the sequence groups shown in FIG.12A and FIG.12B in the form of tables, sequence number calculating section 1002 may calculate the usable sequence number r by looking up these tables. An example method of determining the sequence number r using these tables will be explained below. For example, with an assumption that the reference sequence length Nb is fixed, tables are prepared for the two parameters of sequence length N and reference sequence number rb, and selectable r's are described therein. In this example, radio mobile station apparatus 100 receives the sequence length N and reference sequence number rb signaled from radio base station apparatus 200, refers to the tables associated with these items and determines a Zadoff-Chu sequence that should be used as a reference signal by selecting in a random manner one of the described values that r might assume. Also, an example case has been described above with the present embodiment where parameter determining section 1003 selects one of usable sequence numbers r's based on the frame number or slot number, However, the present invention is not limited to this, and parameter determining section 1003 may select the minimum or maximum sequence number from usable sequence number r's. (Embodiment 2) The sequence allocating method according to Embodiment 2 of the present invention is based on the cross-correlation characteristic of ZC sequence ascertained by computer simulation by the present inventors. FIG.16 is a diagram illustrating the cross-correlation characteristic of ZC sequence ascertained by computer simulation by the present inventors. In FIG.16, the horizontal axis represents the difference of r/N between ZC sequences of different transmission bandwidths or different sequence lengths, and the vertical axis represents the cross-correlation characteristic. As shown in FIG.16, if the difference of r/N between ZC sequences of different transmission bandwidths or different sequence lengths is 0.0, the cross-correlation between ZC sequences is the largest, and, if the difference of r/N is 0.5, the cross-correlation between ZC sequences forms a peak. That is, the cross-correlation between ZC sequences of different transmission bandwidths or different sequence lengths increases when the difference of r/N is closer to 0.5. The sequence allocating method according to the present embodiment has a feature of excluding a ZC sequence that makes a difference of r/N from the reference ZC sequence close to 0.5, from a sequence group. FIG.17 is a flowchart showing the process of the sequence allocating method in a cellular radio communication system according to the present embodiment. Here, in the process in FIG.17, the same process as in FIG.8 will be omitted. In ST 201, as an existing sequence group, a sequence group formed with ZC sequences, in which the difference between r/N and rb/Nb is equal to or less than 1/26 regardless of the number of RB's, is inputted. In ST 202, according to following equation 8, the threshold Xth2(m) is set in a case where the number of RB's is m. That is, Xth2(m) is set higher by a predetermined value every time the number of RB's increases. Xth2(m)=(m-l)x0.0012 ...(Equation 8) In ST 203, whether or not r and N satisfy following equation 9 is decided. ||r/N-rb/Nb|-0.5|