PURPOSE: To reduce greatly the time needed for diagnosis of various memories and also to attain the reduction of load in an execution mode of memory diagnosis as well as the improvement of the memory diagnosis processing efficiency, by providing an autonomous diagnosis function of memory into a controller to be diagnosed.

CONSTITUTION: When a processor memory RAM within an SWC is diagnosed by an MCP, the MCP sends an automatic test order for processor memory to the SWC. Thus a CPU executes autonomously a collation test to a desired data pattern through read/write operations of all available address areas within an RAM area and stores the result of this test to an ANSQ. The MCP obtains the desired timing after transmission of a processor memory diagnosis command and sends an ANSQ reading order to know the result of the diagnosis of the processor memory. In the diagnosis mode of an SCMP, an HCM and SCMS within a TDNW, the MCP designates only the type of a memory and sends a diagnosis command to the SWC. While the CPU within the SWC monitors the contents of an ORDQ like the detection mode of the processor memory diagnosis command and then detects a diagnosis command.