The motor driving circuit includes a first converting circuit that outputs an analog voltage proportional to a rotational speed of a motor, a differential voltage calculating circuit that calculates a differential voltage between the analog voltage and a rotation instruction voltage that prescribes the rotational speed of the motor and outputs a differential voltage signal including information on the differential voltage, a duty controlling circuit that outputs, based on the differential voltage signal, a duty controlling signal including information on a control duty that controls a duty of a PWM signal so as to bring the differential voltage between the rotation instruction voltage and the analog voltage close to zero, and a motor driving waveform controlling circuit that generates the PWM signal in response to a signal based on the duty controlling signal and that outputs the PWM signal.