SERVO TRACK WRITING DEVICE

PURPOSE: To write servo data in a nearly round state with high accuracy by measuring displacement in the radial direction of a magnetic recording medium, calculating an average value of measured values and a displacement amt. and correcting a head position in response to the displacement amt. CONSTITUTION: After a spindle motor 1 becomes its steady rotation, an average value/correcting amt. calculating device 12 is instructed to start operation by a servo track writing control circuit 13. A displacement amt. calculating device 11 and a displacement amt. measuring device 10 are started up by the device 12 to measure displacement in the radial direction of a servo information recording medium 3. Subsequently, a displacement amt. is calculated by the device 11 based on measured data obtained by the device 10, and a correcting amt. is calculated by the device 12 based on the replacement amt. and is sent to the circuit 13. By this method, irregular variations in the radial direction of the medium due to swing of a shaft of the spindle motor is corrected, and hence the write can be carried out with high accuracy.