To provide a disk drive in which write clock that is synchronized to the fluctuation of the revolving speed of a SPM (spindle motor) is generated without providing a special signal pattern or the like and a highly reliable write operation is realized.

A write clock generating circuit 6 generates a write clock which is synchronized to the fluctuation of the revolving speed of a SPM 2 employing dummy read data signal DRD obtained by a dummy read operation immediately prior to a write operation. In the write operation, an encoder 11 outputs write data signals with the timing of the write clock from the circuit 6.