PURPOSE: To adjust the overlapped phase and the phase inversion by comparing a phase of a data readout pulse and a phase of a data write pulse so as to adjust the phase shift in response to the direction of phase shift.

CONSTITUTION: A readout pulse 2 is differentiated by a leading edge differentiation circuit 10a and a trailing edge differentiation circuit 10b. The leading edge and trailing edge differentiation pulses 4, 5 are compared with the phase of the write pulse 3, a state C of the leading edge differentiation pulse 4 overlapped with the write pulse 3 is detected as a read slip 6" and a state D of the trailing edge differentiation pulse 5 overlapped with the write pulse 3 is detected as a write slip 6'. If the read slip 6' or the write slip 6" takes place, a selector 7 changes over the selection to the phase of a write pulse 3" to control the pulse in a direction that the interval of the generation of the write pulse 3 is decreased.