PURPOSE: To prevent users from arbitrarily locking, by providing a locking device of which lock-plate is engaged with a bolt to fix it in the retracted condition, when the bolt is inserted after merchandise have been taken out.

CONSTITUTION: When a user puts in a specified number of coins, in a locked state, a lever 46 prohibiting the rotation is turned and a protrusion 48 prohibiting the rotation is turned to the releasing rotary direction of the driving plate 17 and a control tab 12 can be turned to the releasing direction. When a user turns the control tab 12 to the unlocking direction, a bolt 14 to fit to the driving plate 17 is inserted and released from the door. Then the door can be opened and merchandise can be taken out. When the bolt 14 is inserted, the fixing protrusion of the lock plate is engaged in the fixing groove 34 of the bolt 14 and the bolt 14 is fixed in the recessed state. And hence, it prevents users from arbitrarily locking.