PURPOSE: To obtain torque, by causing expansible and contractible arms to support magnets which also function as weights.

CONSTITUTION: When magnets 6 face a magnet belt 8, a repulsive force is caused between the belt and some magnets 6 to push expansible and contractible arms 4 inwards and an attractive force is caused between the belt and the other magnets 6 to push the magnets in directions shown by arrows in the drawing, so that the arms are revolved while being shortened. As soon as the expansible and contractible arm 4 is released from the magnet belt 8, the arm is elongated. For that reason, the moment of rotation is produced by the length of the descending arm 4 to turn a rotary shaft 1.