PURPOSE: To simplify a circuit configuration, to reduce in size and to improve reliability.

CONSTITUTION: The trouble diagnosing device for a motor driver comprises a power source 75, motor coils 73, 74 connected to the power source 75, driving circuits 71, 72 connected to the coils 73, 74 to excite the coils 73, 74, and motor control means 61 for controlling the circuits 71, 72. The device also comprises a divided voltage detector 8 for dividing a driving voltage between the power source 75 and the coils 73, 74 to be detected to output a detection signal of the detected voltage of a predetermined voltage or lower corresponding to the driving voltage. Further, the device also comprises trouble discriminating means 62 receiving the detection signal of the detector 8 to output a normal signal when the detected voltage coincides with a preset normal voltage and an abnormal signal when it does not coincide therewith.