The invention provides a locking device which comprises an inserting box, a plug, a self-resetting key cylinder and a rolling locking piece, wherein the self-resetting key cylinder and the plug are slidingly connected in the mean axis direction of the plug; inverted cone shaped keyholes for allowing the plug and the self-resetting key cylinder to be inserted into are formed in the inserting box; an accommodating through hole with a side opening is formed in the self-resetting key cylinder; the rolling locking piece is arranged in the accommodating through hole; locking piece guide mechanisms matched with each other are arranged between the self-resetting key cylinder and the plug; under the inserting locking state, the rolling locking piece protrudes out of the side wall of the self-resetting key cylinder and can clamp openings of the inverted cone shaped keyholes. According to the locking device, through sliding fit of the plug and the key cylinder, the rolling locking piece is enabled to be protruded out of the key cylinder or retract into the key cylinder during the inserting and pulling processes to further realize the purpose of controlling the locking state of the locking device through controlling relative sliding of the plug and the key cylinder, so that the inserting and pulling processes are convenient and rapid, and the tight locking force is high without interfering an electronic product.