A motor drive device has: a power supply line to which a power supply voltage is applied; a ground line to which a ground voltage is applied; and a first motor driver that, when the power supply voltage is normal, rotates an N-phase first motor (where N is an integer of 2 or more) by using the supply voltage and, when the power supply voltage is abnormal, generates a rectified voltage from phase voltages of different phases appearing while the first motor is idling to regenerate the rectified voltage to the power supply line. The first motor driver, when generating the rectified voltage, synchronously rectifies the phase voltages of the different phases according to the results of their comparison with the rectified voltage and the ground voltage. The first motor driver is structured so as to rectify the phase voltages of the different phases synchronously in accordance with results of comparison between the phase voltages of the difference phases, the rectified voltage, and the ground voltage.