Abstract: The occurrence of a failure in any of an operational processor and a standby processor is monitored, and when a failure occurs in the operational processor, switching to the standby processor is made. A cache memory of each processor has a plurality of ports through which data can be read and written simultaneously. A cache memory controller of the operational processor transfers an update for the cache memory to the cache memory of the standby processor by using a port different from the port used for updating. A cache memory controller of the standby processor writes the received update into the cache memory by using a port different from the port used for updating.