PURPOSE:To reduce the falling component and eccentric component of thermal offtrack and to execute positioning with high accuracy by correspondently storing an index number and correction servo information and reproducing a correction servo signal. CONSTITUTION:With an INDEX signal, which is obtained once a turn, as a reference, a quantization correction servo signal generated from a data surface 13 in one time of rotation is stored to a storage device 7 of a microcomputer 1. At the time of track following-up operation, the INDEX number on the surface 14 is detected and on the basis of the INDEX number stored in the storage device 7 and correspondence relation between the correction servo signals, a correction servo signal 3 is reproduced to be added to a target value at the time of the track following-up operation. Thus, the falling component and eccentric component of the thermal offtrack can be enough reduced and even when the density of a data track is increased, the head positioning of the high accuracy can be executed without damaging a high-speed access.