It is an object to prevent a command-issuing interval from being fixed and then avoid a situation where a target always returns a retry by varying a timing of a command-issuing request (i.e., a request signal) from each initiator, even if a plurality of initiators simultaneously or alternately make a plurality of command-issuing requests (i.e., send request signals). Based on predetermined priorities, a bus control unit sends a grant signal to an initiator that has sent a request signal, thereby granting use of a bus to the initiator. A mask generating unit sends a mask signal to at least one initiator to have the initiator mask a request signal, thereby controlling a timing, at which the bus control unit grants use of the bus to the initiator, to be aperiodic.