To provide epoch-making technology storing inertia energy of a vehicle as energy capable of displaying force to start the vehicle that was thought impossible before.

This energy storage device can store energy and release the stored energy and is composed of a base body 1, a movable body 3 reciprocating in relation to the base body 1 and a magnet body 4 moving with accompanying reciprocating motion of the movable body 3. Two or more magnet bodies 4 are arranged in parallel and gap between the magnet bodies 4 is reduced by reciprocating motion of the movable body 3. Two or more magnet bodies 4 are arranged in such a manner that same poles repulsing each other adjoin. Repulsion energy between each magnet bodies 4 is stored by reducing gap between the magnet bodies 4 arranged in parallel by reciprocating motion of the movable body 3 and the movable body 3 returns by releasing the stored energy.