To provide a simple, versatile locking device for a game machine for preventing a fraudulent unlocking.

This locking device comprises a member to be fastened which is provided on the game machine main body, a locking member 5 which is provided on a front door 2, an unlocking member 6, a link 7 and a hook member 8. The link 7 has a one-directional pin 71 which is driven only on one end of a slot 62 of the unlocking member 6. A movement only in one direction is transmitted between the link 7 and the unlocking member 6 by the one-directional pin 71. Thus, even when a fraudulent unlocking operation is performed to the hook member 8 from the outside, the movement of the hook member 8 is interrupted between the link 7 and the unlocking member 6, and is not transmitted to the unlocking member 6. Therefore, the hook member 8 is not interlocked, and the front door 2 cannot be opened.