An electronic device includes a connector, at least two kinds of signal transmitting circuits, and a selecting system. The connector is capable of transmitting audio and video signals when connected to a peripheral device. The selecting system includes a detecting module, a memory module, a comparing module, and a connecting module. The detecting module is capable of detecting and measuring the voltage of a signal line of the connector. The memory module is capable of storing predetermined voltage ranges corresponding to different kinds of peripheral devices. The comparing module is capable of comparing the voltage of the signal line measured by the detecting module to the predetermined voltage ranges and determining what kind of peripheral device is connected to the connector. The connecting module is capable of connecting the connector to one of the signal transmitting circuits according to the comparing module.