To improve the data hold reliability as a disk drive by decreasing the unnecessary write processing frequency of partition information and decreasing the error occurrence rate.

When a host 1 outputs a write instruction to a predetermined specific address X, a disk control part 2 of the disk drive checks whether or not the data in the address X (address where partition information is written) is present on a data buffer 1, compares data received from the host 1 with the data on the data buffer 11, and does not perform operation for writing to a medium 4 and ignores the write instruction from the host 1 when the both are the same, but performs the operation for writing to the medium 4 when the comparison result shows a discrepancy.