To surely protect a regenerative resistor, in a motor driving device capable of absorbing regenerative power.

The motor-driving device 10 is a device that can absorb regenerative power from a motor and comprises an inverter portion 12, the regenerative resistor 13, a first semiconductor switch element 14, a second semiconductor switch element 15, a voltage-detecting portion 23, and a system control portion 20. The motor driving device drives a motor with variable speed by using direct current. The regenerative resistor is connected in parallel with the inverter portion and absorbs regenerative power. The first semiconductor switching element is an element connected in series with the regenerative resistor. The second semiconductor switching element is an element connected in series with the first semiconductor switching element. The voltage detecting portion detects a supplied direct-current voltage. The system control portion controls the first and second semiconductor switching elements according to the result of detection by the voltage-detecting portion.