Abstract: A detection device for contact fusion in an electromagnetic contactor in which an electric motor is connected by way of main contact of an electromagnetic contactor on the secondary side of a breaker equipped with electronic tripping device has a detection circuit for the voltage applied to the electromagnetic contactor coil connected in series with a pushbutton switch and a detection circuit for the voltage applied to the electric motor; a relay coil of a relay for detecting the contact fusion is connected to the tripping coil of the breaker and an ON-OFF element for supplying or interrupting the supply of an electrical current to the coil and a control circuit for the ON-OFF element are connected to the detection circuit for the voltage of the electrical motor both of the detection circuits are coupled with each other by a photocoupler, whereby the ON-OFF element is turned ON when the pushbutton switch is turned OFF in the case of the fusion of the main contacts, thereby exciting the relay coil to turn the