PURPOSE: To reduce the power for cooling by using a thyristor in the input power supply control section of a power supply for cooling a superconducting material, and inserting the superconducting material between the gate and the cathode of the thyristor.

CONSTITUTION: A thyristor 4 is used in the input power supply control section of a power supply for cooling a superconducting material, and a superconducting material 7 is inserted between the gate and the cathode of the thyristor 4. For instance, thyristors 4A, 4B are connected to the input side of an a.c. motor 3 for driving a compressor 2 which feeds a coolant into a cooler 1 for superconduction, superconducting materials 7A, 7B are inserted between the gate and the cathode of the thyristors 4A, 4B, and the superconducting materials 7A, 7B are placed in the cooler 1. With this, above the critical temperature, the superconducting material 7 exhibits a resistance and a current flows in the thyristor 4, whereby the cooler 1 is cooled. And, below the critical temperature, the resistance value of the superconducting material 7 becomes zero and the control power supply becomes inoperative, whereby the power consumption for cooling can be reduced.