Battery charger for portable electronic equipment

There is offered a battery charger for a portable electronic device that has a simple structure and is capable of detecting that the portable electronic device is connected to the battery charger. A first power supply line 13 is connected to a positive terminal (+) of a rechargeable battery 10, while a ground line 15 is connected to a negative terminal (-) of the rechargeable battery 10. An output transistor 11 is connected between the first power supply line 13 and a second power supply line 14. The output transistor 11 is connected to a Vbus terminal of a USB connector 12 through the second power supply line 14. A controller 20 outputs a voltage of an H level to the Vbus terminal to detect a change in a voltage at the Vbus terminal, and judges whether the portable electronic device 30 is connected to the USB connector 12 based on a result of the detection. The controller 20 turns the output transistor 11 on when the portable electronic device 30 is judged to be connected to the USB connector 12.