The present invention provides a locking apparatus for switching between a lock state and an unlock state of a sliding device in a system. The system has a plug and a socket. The sliding device has a shaft. The locking apparatus has a sliding member, a spring, a hook, and a connecting member. The hook has an end part and a bending portion for locking the shaft. When the plug is plugged into the socket, the locking apparatus unlocks the shaft. When the plug is pulled out from the socket, the locking apparatus locks the shaft.