PURPOSE: To obtain a protecting device capable of interrupting bipolar currents, when a superconducting coil for bipolar current conduction is quenched.

CONSTITUTION: The title protecting device for superconducting coil has a DC interrupting part composed of a parallel circuit of a first commutation circuit composed of a first commutation capacitor 41 and a first closing switch 51 connected in series to this, a second commutation circuit 42 composed of a second commutation capacitor 42 to be charged to a polarity reverse to that of the first commutation capacitor 42 and a second closing switch 52 connected in series to the capacitor 42, and a DC circuit breaker 3. Besides, it has a detector 7 for detecting the quench of the superconducting coil 1, a current measuring device 9 for detecting the coil current, and a controller 81 for performing the closing control of the first and second closing switches 51 and 52 in accordance with the signals from these instruments.