A motor drive device includes an inverter circuit, a driver circuit for outputting a PWM signal to the inverter circuit, a booster circuit for boosting a power supply voltage supplied from a power supply circuit, a fail safe circuit arranged between the inverter circuit and the motor, and a fail safe drive unit for outputting a signal for turning ON/OFF a semiconductor switching element of the fail safe circuit. A boost voltage output from the booster circuit is supplied to the driver circuit and also supplied to the fail safe drive unit. The fail safe drive unit drives the semiconductor switching element of the fail safe circuit by such boost voltage.