An electricity storage system includes a plurality of storage modules connected in series, each storage module including a single storage cell or a plurality of storage cells connected in series, an isolation transformer and a rectifying circuit that are associated with each of the storage modules, the isolation transformer having a primary winding and a secondary winding, and a voltage balancing circuit that generates an alternating current by switching a direct-current power source, the primary windings of the isolation transformers being all connected in parallel and connected to an output end of the voltage balancing circuit by a common wiring, the secondary windings of the isolation transformers being connected to the corresponding storage modules via the respective rectifying circuits, the alternating current being supplied to the primary winding of each of the isolation transformers.