A drive control signal is effectively obtained. An offset is added to a rotational state signal. A drive control signal having a period which is reduced by a predetermined period compared to the sine wave form signal is generated between a crossing of a reference value for a second time and a crossing of the reference value for a next time by an added signal obtained by sequentially offsetting the rotational state signal in a direction reaching the reference value. A pulse indicating that the polarity has been reversed when the offset is added is added to the crossing of the reference value for the first time, to reliably detect crossing of the reference value for the second time.