Safety against error setting of a primary battery in a dedicated battery charger for secondary batteries can be assured even when the battery charger is of a timer type advantageous for cost reduction. A switching circuit (2) is connected between terminals (13, 15), and terminals (14, 16) are connected. Terminals (15, 17) are connected, and terminals (16, 18) are connected. The positive pole of a battery (3) set in position is connected to the terminal (17), and the negative pole is connected to the terminal (18). A battery discriminating circuit (4) connects to the positive pole and the negative pole of the battery (3) set in position; and judges whether the battery (3) is a primary battery or a secondary battery. Depending upon the result of the discrimination, the battery discriminating circuit (4) supplies a switching signal to the switching circuit (5) to turn it on or off. A capacitor (6) and a resistor 7 are connected in parallel between a timer circuit (9) and a ground potential. The switching circuit (5) and a resistor (8) are connected in series between the timer circuit (9) and the ground potential. Once the switching circuit (2) turns on, a constant voltage source circuit 1 supplies a charging direct current to the secondary battery.