1. A frequency block allocation method for a radio communication system in which one or more radio stations and mobile stations perform radio communication using a frequency block selected from a plurality of system bands, the frequency block allocation method comprising:determining number of component carriers that can allocate to each mobile station;
calculating a communication band index, indicating an expected value of a band to be allocated for the each mobile station, based on bandwidths and loads of the component carriers according to the determined allocation number of the component carriers;
calculating an allocation index, which is expected upon allocation of the frequency block to the each mobile station, for each of the component carriers using the communication band index, an instantaneous rate and an average rate, which are expected upon allocation of the frequency block to the each mobile station; and
allocating frequency blocks to the each mobile station based on the allocation indices.