The disk controller has a plurality of channel control units, a plurality of cache memories, a plurality of disk control units, and a plurality of internal switch units. Each channel control unit or disk control unit sends to one of the cache memory units a request packet requesting execution of processing. The cache memory unit sends a response packet in response to the received request packet. Each internal switch unit monitors the request packet sent from the channel control unit or disk control unit, and judges whether or not the response packet to the request packet has passed through the internal switch unit within a first given time period since the passage of the request packet. In the case where the response packet has not passed through the internal switch unit within the first given time period, the internal switch unit sends a failure notification.