First and second A/D converters perform analog/digital conversion of first and second signals of a Hall signal so as to generate third and fourth signals as digital signals. A differential conversion circuit generates a fifth signal as a single-ended signal that corresponds to the difference between the third and fourth signals. An offset correction circuit corrects offset of the fifth signal so as to generate a sixth signal. An amplitude control circuit stabilizes the amplitude of the sixth signal to a predetermined target value, and generates its absolute value, thus generating a seventh signal. A control signal generating unit generates a control signal based upon the seventh signal. A driver circuit drives a motor according to the control signal.