A voltage adjuster has: a current path connecting one end on an input/output terminal side and the other end on a secondary battery side; a bypass path of the current path; a converter provided in the bypass path and capable of changing input electric power to a predetermined voltage corresponding to the secondary battery or a predetermined voltage corresponding to an external device in accordance with the charge or discharge of the second battery; and a path selector configured to select a path to be used out of the current path or the bypass path in accordance with the charge or discharge of the secondary battery.