To provide a device for control of an electric motor having a braking resistor circuit, capable of preventing malfunction of resistive braking, by obtaining a larger device capacity, even if power fluctuation of an AC power supply is large.

The device is constituted of a converter 2 which converts an AC voltage of an AC power supply 1 into a DC voltage and has a smoothing capacitor 3 on the output side, an inverter 4 which inverts a DC voltage into an AC voltage and drives a motor 5, a braking resistor circuit 6 constituted of a series circuit of a resistor 61 and a switching element 62, an inverter controller 20, and a brake controller 10. When the output voltage of the converter 2 reaches or exceeds a first predetermined voltage which is lower than the DC voltage when the power supply voltage of the AC power supply 1 is highest, and the torque reference of the inverter controller 20 or the polarity thereof is negative, the brake controller 10 operates the switching element 62 so that the regenerative electric power supplied from the motor 5 is absorbed by the resistor 61.