A motor driving device that drives a motor with an alternating-current power converted from a direct-current power supply, includes an inverter that receives a pulse-width modulation signal and supplies the alternating-current power to the motor, and an inverter control unit that generates the pulse-width modulation signal and supplies the pulse-width modulation signal to the inverter. The inverter control unit reduces the number of pulses of the pulse-width modulation signal generated during a first period within one period of a mechanical angle of the motor to be lower than the number of pulses of the pulse-width modulation signal generated during a second period within the one period of the mechanical angle of the motor. The first period is a period during which a load torque is lower than a load torque during the second period.