An energy storing device is disclosed. In the energy storing device of the present invention, energy from an energy generating unit is stored in the form of spring torsion and then is output steadily. The energy storing device of the present invention includes a plurality of cog-wheels, a plurality of torsion magnitude limiting units, a plurality of single-directional input bearings, a plurality of energy storing units and a plurality of speed enhancing cog-wheels. Each of the energy storing units includes at least two end rotational disc portions, which are connected with each other co-axially. A leaf spring unit is provided between each pair of rotational disc portions and one end of the leaf spring unit is bent in an opposite direction. In addition, the energy storing units may be connected in series or in parallel to increase the efficiencies in energy storage and energy output.