PURPOSE: To realize a magnetic disk subsystem with high reliability by providing plural memory controlling circuit on one cache memory, in a magnetic disk subsystem with a cache memory.

CONSTITUTION: A magnetic disk subsystem 3 is constituted of one piece of cache memory 6, and two pieces of ECC.memory controlling circuits 7A, 7B which are connected in parallel to said memory. The ECC.memory controlling circuit 7A is connected to a magnetic disk control device (DKC) 4A, and on the other hand, the controlling circuit 7B is connected to a DKC 4B. Both of them execute the control of operation of the memory part 6, generation of an error code at the time of write of information against said control, and the correcting operation of an error at the time of read-out. Both the DKC 4A and 4B are connected to a host 9 and a magnetic device 5, and control a mutual transfer operation, etc. of storage information between these devices and the cache memory 6.