PURPOSE: To always execute phase synchronizing except when a sector pulse is logical '1', at the time of selecting a head, and at the time of seeking in the case a phase synchronizing oscillation circuit phase-synchronizes with a readout signal from a storing medium.

CONSTITUTION: A sector pulse signal 3, a seeking signal 4 and a head selecting signal 5 are connected to a 1st control circuit 9 to express a phase-synchronizing condition. A signal outputted from the circuit 9 and a byte clock signal 6 where rectangular waves are continued are counted by a counter circuit 10 and outputted as an internal phase synchronizing control signal 1c. The signal 1c and a phase synchronizing control signal 2 are connected to a 2nd control circuit 11. The circuit 11 is connected to a phase synchronizing oscillation circuit 12 and judges based on the signals 1c and 2 whether or not the phase synchronizing with the storing medium can be possible, and outputs a phase synchronizing control rise signal 1a and a phase synchronizing control fall signal 1b.