A disc array device receives a hardware diagnosis after shipment of the disc array device at short times during an operation of the device and a diagnostic rate is enhanced and an internal failure of a LSI can be detected at a device level. By at least one MP of a redundant-constitution channel interface control adaptor, a hardware diagnosis of a part in a channel interface control adaptor is made, and hardware diagnoses of a part in a CACHE and a part in a cache path switch are made through a diagnostic interface. By at least one MP of the redundant-constitutional disc drive interface control adaptor, a hardware diagnosis of a part in the disc drive interface control adaptor is made, and hardware diagnoses of a part in the CACHE and a part in the cache path switch are made through a diagnostic interface.