PURPOSE: To efficiently process access requests from plural request origin devices by resetting the access request from another request origin device for an address on which a certain request origin device desires to execute to make access exclusively.

CONSTITUTION: When request information is set on a request register 1, the request information and a register number are set on a request port 5 at a request selection part 25 according to a priority order. The address to which a certain request origin desires to execute to make access exclusively and the register number are set on a lock register 15, and they can be cancelled by a cancel request from the same request origin device. A comparator 14 compares the lock register 15 with the content of the request port 5, and outputs a signal when the register numbers are different and their addresses are the same. A precedence control part 22 resets the request port according to the signal. At this time, a lock control part 21 blocks the set of the request register 1, and holds the request information.