To provide life extension for a battery by enabling supply of large current even if remaining battery capacity drops and preventing an excessive stress from being given to the battery, to attain reductions in battery size and weight and high safety during running by controlling running charging so that a remaining battery level may be within a stably operable range, for example, during running on a flat road requiring only a small pedaling effort, and to eliminate charging operations from a commercial power source, using solar battery charging from a bicycle.

An electric double-layer capacitor and a converter for driving an assist motor are provided in parallel to each other, and the battery is connected to the electric double-layer capacitor through a reactor, a current detector and a switch opening and closing in response to a current value.