To suppress fluctuant rotational speed and uneven rotation of a rotation body while reducing rotational torque and shortening time for obtaining a condition of uniform rotary motion.

This device positions a plurality of weights 62, 63, 64, 65 movable in a diametric direction of a flywheel main body 61 mounted in a rotation body 80 by means 67, 68, 69, 70 giving a moving habit to a rotational center side of the flywheel main body 61 when the rotation body is stopped. Each weight is positioned in the rotational center side, when the rotation body 80 is stopped, and moved in a diametric direction of the flywheel main body 61 by centrifugal force, when the rotation body 80 is rotated, to make rotational moment variable.