PURPOSE: To provide a flywheel having low energy loss and convenient for handling and an electromagnetic prime mover having a high efficiency using the flywheel.

CONSTITUTION: A flywheel comprises a connecting rod supported at its center to a rotary shaft of various machines, and heavy weights mounted at both ends of the rod. An electromagnetic force prime mover comprises a pair of electromagnets A-D disposed oppositely, attracting plates 6a, 6b of magnetic materials disposed in spaces S between the electromagnets A-D, a force couple lever 4 rotatably mounted at a stationary shaft 5, a rod 8 mounted at its one end at the lever 4 and at the other at a crank 9 to reciprocate in cooperation with the lever 4, and a flywheel 20 mounted at a crankshaft 9a of the crank 9.