PURPOSE: To check the abnormal temperature rise, by changing over a switching element to the non conducting state when the counted value of a counting means gets to the upper limit value in the regenerative braking period.

CONSTITUTION: An inverter 17 is composed of a full-wave rectification circuit 11 as a power rectifier, a smoothing capacitor 15, and an inverter main circuit 16 as a power inverter. A regenerative power absorption circuit 19 connected between DC bus bars 14A and 14B is composed of a DC body with a resistor 20 and a transistor 21. Further, the inverter 17 is equipped with a resistor voltage detection circuit 22, a power supply voltage detection circuit 28, a regenerative brake control circuit 34, a state detection circuit 40 as a counting means, a damage detection circuit 46, a switching control circuit 49 and a power supply circuit 50 to control a switch 13. In the period the detected voltage is above the set voltage, every fixed value is added, while in the period the detected voltage is below the set one, every fixed value is subtracted, so that in the period when it is more than the upper limit value, the above transistor 21 is changed over to a non conducting state.