When a testing system is connected to a debug port of a tape drive unit or a SCSI bus, a self-checking test for a fabricating process is executed. When the testing system is not connected, the self-checking test for normal operation is executed. And in a test of a single card, a motor test and an MR head resistance test, which are tests of a mechanical structure portion, are omitted. In addition, in a box assembling process, the test contents are suppressed to a minimum prior to adjustments to the, tape head. Furthermore, in a test program, the status of a flag or an indication corresponding to a test executed in a next step is changed.