PURPOSE: To quickly inspect the cause of a fault relating to a buffer by managing the history information of the buffer to be used for communication.

CONSTITUTION: When a buffer securing request is outputted from a communication control part 10 at the time of communication processing with a host device 2, a buffer managing part 11 allocates an idle buffer in a buffer part 12 to the request. Simultaneously, the managing part 11 stores the address and time of a module receiving the buffer securing request in a buffer information storing part 13. On the other hand, when a buffer releasing request is outputted from the control part 10 at the end of communication processing, the managing part 11 releases the buffer allocated to the request in the buffer part 12. Simultaneously the managing part 11 stores the address and time of a module requesting the buffer release in the storing part 13.