A radio communication system includes a base station device and a plurality of mobile station devices which radio-communicate with the base station device. The base station device allocates random access signal identifiers for identifying random access signals to the mobile station devices and decides an allocation period for each of the random access signal identifiers used by the mobile base stations. During the allocation period, each of the mobile station devices transmits a random access signal corresponding to the allocated random access signal identifier. Thus, it is possible to suppress a delay until the random access procedure using a dedicated preamble is complete.