PURPOSE: To accurately detect an abnormality in the armature coil of a DC motor by providing a circuit for extracting a current change component due to the disconnec tion of the armature coil, from the output of a current transformer and detecting the abnormal state in the armature coil by the current changed component.

CONSTITUTION: When the armature coil of a DC motor 1 is broken, the value of an armature IA widely decreases at every revolution of an armature. Thus, since the detection current ID of the current transformer 7 of a current change detecting circuit 4 takes a current waveform wherein a DC component is cut off and supplied to an LPF 9, only a frequency component smaller than the cut off frequency of the current ID is extracted by the LPF 9. As a result, only the current change components due to the disconnection of the armature coil are outputted IL from the LPF 9. The output IL of the LPF 9 is full-wave-rectified 10 and rectified output is supplied to an integrat ing circuit 11. The output II of the circuit 11 gradually increases at every arrival of the current change component due to the disconnection of the armature coil. At a moment when the output II exceeds a value IS as set 12, the output AS of a compari son circuit 13 is inverted from a logical value '0' to '1'. Thus, an alarm sound or the like is emitted from an alarm circuit 14.