A battery charger for charging a secondary battery using a power supply circuit, includes a discrimination circuit to discriminate a constant-current charging mode and a constant-voltage charging mode, and a controller to which a discrimination signal is supplied. When judged as being the constant-current charging mode, the controller sets the current in the constant-current charging mode by using the control signal. When judged as being the constant-voltage charging mode in accordance with the discrimination signal, the controller sets intermittently the end of charging detection current, and sets an end of charging detection period for judging the constant-current charging mode and the constant-voltage charging mode. When the discrimination signal indicates the constant-voltage charging mode in the end of charging detection period, the controller controls to shift to the end of charging detection mode.