The utility model provides a locking device used for a tool box. The device is characterized in that a supported hole (1) and a protection box (7) fixed on a box body are included, a rotating shaft (2) is mounted on the supported hole (1), a lock hook (3) and a rotating plate (4) are fixed on the rotating shaft (2), the rotating plate (2) is connected to one end of a spring (5), the other end of the spring (5) is connected and fixed on a fixing plate (6) on the box body, a padlock (8) is arranged in the protection box (7), a hook (9) of the padlock (8) is fixed in the box body, and the end on which the hook (9) is mounted of a padlock body (10) of the padlock (8) is in contact with the rotating plate (4). The security of the device is very high, at the same time, the use of the padlock to lock a tool box for users is very convenient and low-cost, and the padlock can be conveniently replaced in the event of loss.