PURPOSE:To obtain a sector mark signal on a sector from which the sector mark is not read by outputting a sector mark reading signal by a reading means, and a pseudo signal generated from a pseudo signal generating means as the sector mark signals. CONSTITUTION:On the sector of the respective sectors of a disk 3 from which the sector mark is read by a head 2, the sector mark reading signal (a) is pro vided to an inspection unit as the sector mark signal as it is from a device 1. On the sector of the respective sectors of the disk 3 from which the sector mark is not read by the head 2, the pseudo sector mark signal (e) generated from the pseudo sector mark generating circuit 9 is supplied to the inspection unit as the sector mark signal. In the inspection unit, based on this sector mark signal, the respective sectors of the disk 3 are inspected. Thereby, the inspection can be performed to the sector from which the sector mark is not read and the inspection can be efficiently carried out without interrupting it.
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