A motor drive device for driving a motor, which has a plurality of winding pairs, includes a plurality of inverter units for the plurality of winding pairs. The inverter units are coupled in parallel to a power source. A plurality of capacitors provided for the plurality of inverter units, and a plurality of power relays are disposed between the power supply and the inverter units. In particular, a power relay is provided for each of the inverter units. A control unit detects a short failure of the power relay, and simultaneously turns ON the power relays that do not have a short failure. In such manner, damage to the power relays as well as damage to other electronic components of the motor driver device due to a large electric current is prevented.