Abstract: A damping mass is housed in a rolling chamber formed in a flywheel body, and executes a pendulum motion in a radial direction according to torque fluctuations. If md is the mass of the damping mass, Id is tile moment of inertia of the damping mass, rd is the radius of tile damping mass, n is the order of torque fluctuations of a rotating drive mechanism, R is the distance from the center of rotation of the body to the center of the pendulum motion of the damping mass, and L is the distance from the center of the pendulum motion of the damping mass to the center of gravity of same, the actual ratio R/L is set larger than a value Ro/Lo obtained from the theoretical relation Ro/Lo=n.sup.2. [1+{Id/(md.multidot.rd.sup.2)}] to reduce rotational fluctuations. In this way, the effect of manufacturing defects and dimensional variations due to wear on rotational fluctuations is reduced.