PURPOSE: To produce sufficient torque through a simple structure by employing a screw-shaped rotor made of a superconductor and rotating the rotor in a field generated by a solenoid coil.

CONSTITUTION: A field solenoid coil is placed in a cooling vessel filled with a refrigerant and a space (bore) for containing a rotor 16 is formed in the center thereof. The solenoid coil is formed by winding a superconducting wire and rendered superconductive in the refrigerant. A rotor 16 has a drive shaft 14 fixed, on the circumferential surface thereof, with a plurality of screw blades 30. The screw blade 30 comprises a blade base 30a made of a nonmagnetic material, and a superconductor 30b formed on the surface thereof. The superconductor 30b is formed by laminating a superconducting material on the blade base 30a. When a permanent current is fed to the solenoid coil, a field B is formed directing upward. Reaction to the field B is generated on each screw blade 30 in the direction perpendicular to the surface thereof and a rotary force is generated.