An electronic device includes a casing, a plug, a retaining element and a resilient element. The casing has multiple support members and multiple receiving parts. The plug has a rotating shaft and multiple pins. The rotating shaft includes a ratchet tenon and is pivotally supported on the support members. The pins are substantially perpendicular to the casing when the pins are rotated to the first position. The pins are received in the receiving parts of the casing when the pins are rotated to the second position. The retaining element includes a ratchet part. The resilient element is contacted with or sustained against the retaining element for providing a restoring force on the retaining element. The ratchet part is engaged with the ratchet tenon of the rotating shaft due to the restoring force, so that the pins are automatically fixed in either the first position or the second position.