PURPOSE: To prevent a battery from being overcharged by connecting the output of a rectifier charging circuit connected in series with a drive coil and a contact which is opened and closed by means of the coil to a chargeable battery and supplying electricity to the coil by means of a definite-time continuity switch for a fixed period of time in the initial stage of charging.

CONSTITUTION: When the alternating current of outside commercial power supply 8 is connected to a battery charger 1, a trigger generation circuit 3 for a definite-time continuity switch 4 generates a trigger pulse and the switch 4 is closed. Then a direct current generated by a rectifier charging circuit 2 starts to charge a chargeable battery 9 through the drive coil 7 of an electromagnetic relay 5 and, at the same time, the drive coil 7 closes a contact 6. The switch 4 is opened after the elapse of a prescribed period of time, but the contact circuit 6 is left closed due to self-holding. When the battery 9 is completely charged, no electric current flows through the coil 7 and the contact circuit 6 is opened, because the output voltage of the circuit 2 becomes equal to the voltage of the battery 9.