To provide a motor drive device that protects a switching element of a drive part from counter electromotive voltage that a motor generates through rotation by an external force under a state where it is not connected to a DC power supply.

A motor drive device 101 includes counter electromotive voltage detection parts 71, 72, and 73 and a protection control part 601. When voltage that the counter electromotive voltage detection parts 71, 72, and 73 detect exceeds a threshold voltage Vt of a Zener diode 64, a voltage signal is inputted into induction gates 541, 551, and 561 via detection signal lines 61, 62, and 63 and sequentially turns on switching elements 54, 55, and 56 of a lower arm. Consequently, current by counter electromotive voltage applied to a drive part 50 flows to the ground through the switching elements of the lower arm under an on state. Therefore, a state is obtained in which a brake torque is produced with respect to rotation of a motor 80 by an external force, so the counter electromotive voltage lowers. As a result, it is possible to protect the switching elements of the drive part 50 from overvoltage.