To reduce the load on bearing applied by pitching or rolling of a vehicle for supporting a flywheel of a large mass which is rotating at high speed, by setting the center of gravity of the flywheel and of the electric motor so that the rotary shaft of the flywheel may be perpendicular while the flywheel is rotating.

A first gimbal 11 and a second gimbal 12 are rotatably connected to each other at right angles with each other and, while the vehicle is pitching or rolling, a rotary shaft 21 of a flywheel 1 and of an electric motor 2 can be so corrected as to be perpendicular by these gimbals 11 and 12. By this method, even if the vehicle pitches or rolls, the rotary shaft 21 of the flywheel 1 and of the electric motor 2 can be automatically corrected so as to be perpendicular, thereby reducing the load to be applied to bearings 22, 23 for supporting the flywheel 1 of a large mass which is rotating at high speeds.