To prevent a collision from occurring at the time of random access in cases such as handover, response to paging and the like where a mobile station apparatus performs random access in response to directions from a base station apparatus. In a mobile communication system in which a mobile station apparatus 200 uses a signature of a beforehand determined signature group at the time of random access with a base station apparatus 100, the signature group is comprised of a signature group managed by the base station apparatus 100 and another signature group managed by the mobile station apparatus 200. The signature group managed by the base station apparatus 100 includes signatures associated with particular random access reasons to be selected by the base station apparatus 100.