A motor driving circuit includes a magnetic-pole-position detecting unit that detects a rotating position of a rotor of a permanent magnet synchronous motor, a voltage output unit that converts a direct-current voltage and generates a driving voltage for the permanent magnet synchronous motor, a voltage control unit that controls the voltage output unit on the basis of a comparison result of a modulation wave and a carrier wave, a voltage-phase adjusting unit that determines, using a differential amplifier circuit that receives a rotating speed control signal and an offset signal, a phase of the modulation wave generated by the voltage control unit and causes the voltage control unit to generate the modulation wave in the determined phase, and an offset generating unit that generates the offset signal.