PURPOSE: To stabilize a seek operation by eliminating an undershoot state, etc., in reference to the shift of an optical spot.

CONSTITUTION: A target velocity generating part 8 calculates the remaining track number TCN including a target track based on the value TC of a counter 6 of track pulses TP and the seek track number N. Then the part 8 generates a target velocity VR proportional to the square root of TCM in a period of TCN>M and also generates the velocity VR proportional to the TCN in a period of TCN≤M respectively. A driving circuit 11 drives a seeking motor 4 in response to the velocity error VE between the velocity VR and the shifting velocity VD of an optical spot.