A brake drive control circuit of a servo motor which detects malfunction of a semiconductor circuit at the brake drive control circuit, that is, a brake drive control circuit which connects two semiconductor circuits in series to a brake and uses a voltage detection circuit which detects the presence of voltage which is applied to the brake by brake signals turning the semiconductor circuits on/off so as to detect test pulses in the voltage which is applied to the brake due to test pulses which are included in the brake signals and turn the semiconductor circuits off for instants during an operation for disengaging the brake and detect malfunctions of the semiconductor circuits by the detection of the test pulses.