PURPOSE: To obtain a system for automatically charging a battery of an automobile extremely simply by an unmanned operation.

CONSTITUTION: A battery charging circuit 2 is provided in a vehicle, and a power source circuit 3 is provided at the side of a passage. A primary coil 5 and a secondary coil 6 are provided in both the circuits, transformer-coupled to supply power. A switch 11 is inserted into the power source circuit, an oscillation coil 10 of a high frequency oscillator 9 is provided on a road surface, a change in an oscillating state due to a change in a mutual inductance when the vehicle is stopped at a specified position on the passage is detected, and its approach is detected to turn the switch 11 on, thereby automatically charging.