Abstract: In accordance with an embodiment, a flywheel includes a rotary shaft which is rotatably provided to the flywheel, a rotor which is fixed to the rotary shaft and rotatable with the rotary shaft, and an unrotatable stator arranged so as to face the rotor. The rotor includes first permanent magnets provided on a first surface facing the stator. The stator includes second permanent magnets which are provided on a second surface facing the rotor in correspondence with the first permanent magnets respectively and have the same polarity as that of the first permanent magnets.