A novel charger wherein a constant electric power control is made such that an electric power feed at the output end is the same as the electric power fed by a fuel cell at the input end, thereby keeping a cell charge current constant, reducing the number of components and further realizing a stable charging. A charger, an input source (Vfc) of which is a fuel cell or solar cell exhibiting a relatively large output impedance during electric power feed, includes a secondary cell (B) at the output end. A current control circuit (10), which is connected to the secondary cell, supplies a charging current to be caused to flow into the secondary cell. The value of the charging current is obtained from a control amount necessary for maintaining a converter output voltage at a drooping voltage as set.