Hardware diagnosis of a disk array apparatus is conducted before shipment by using a self-diagnosis circuit, using the same criteria that apply to actual [in-use] equipment. A logical circuit 18 and a self-diagnosis circuit 22 are mounted on an LSI 10. When a test program is loaded to a RAM 28 and a diagnosis command is input to a CPU 26 before shipment, a pattern generation circuit 24 generates a pattern and expected value pattern data corresponding to the pattern under the control of the CPU 26. When the pattern is input to the logical circuit 18, the logical circuit 18 operates according to the pattern and outputs pattern data showing the test result. An expected value checking circuit 30 compares and checks this pattern data against the expected value pattern data and then outputs the diagnosis result regarding whether the logical circuit 18 is normal or abnormal. The content of the diagnosis result is displayed on an external display unit.