To accurately discriminate a size-AAA battery and a size-AA battery while extremely simplifying a circuit configuration.

A charger has a selector circuit 2 for the size-AAA battery 1A and the size-AA battery 1B. The selector circuit 2 has a detecting resistor 6 connected in series with the size-AAA battery 1A, a voltage detector 4 detecting the voltage of a parallel circuit connecting the size-AA battery 1B in parallel with the series circuit of the detecting resistor 6 and the size-AAA battery 1A and a current supply circuit 3 changing over a first detecting current and a second detecting current having different current values and supplying the parallel circuit with the changed-over detecting current. The selector circuit 2 further has a discriminating circuit 5 discriminating the size-AAA battery 1A and the size-AA battery 1B from a voltage difference of the detecting voltages of the voltage detector 4 under the state supplied with the first detecting current and the second detecting current. The selector circuit 2 discriminates the size-AAA battery 1A and the size-AA battery 1B from the first detecting voltage in the first detecting current detected by the voltage detector 4 and the second detecting voltage in the second detecting current under the state supplying the parallel circuit with the first detecting current and the second detecting current by the current supply circuit 3.