of the next servo pulse interval based on the variation information obtained from about 5 of these servo sectors or 5 to 10 servo sector pulses fig5 is a flowchart indicating an example of the operation of data sector pulse generation section 21 according to this method the disk control unit 7 activates the data sector pulse generation section 21 in the id generation unit 15 step s 10 and sets an optimum variation u03b4l to the data sector pulse generation control register block 22 in the id generation unit 15 based on a servo sector interval predicted as mentioned above step s 11 in response to this the data sector pulse generation counter correction block 31 in the id generation unit 15 calculates a corrected data sector pulse counter value a u2032 from a preset normal data sector pulse interval and the variation u03b4l step s 12 for example a u2032 may be calculated as a u2032 1 u03b4l u00d7 a if the servo sector pulse reception block 23 in the id generation unit 15 receives a servo sector from the servo sector unit 16 step s 13 the internal counter 24 of the data sector pulse generation block 26 begins to count step s 14 when the counter reaches the corrected counter value a u2032 step s 15 calculated in advance the data sector pulse generation block 26 outputs an data.