To find wrongdoing easily, by actuating the stopper drive means of the stopper opening/closing device of each pachinko machine by the use of an instruction means actuated by a responsible person in charge, and by releasing a stopper from the locking means of a front frame.

By turning a stopper 41 upward by means of a motor M and locking it into a position, a switch actuation piece 47 presses a contact piece 50, so that a switch is turned on. On the other hand, by turning the stopper 41 downward and releasing the lock, the switch actuation piece 47 moves apart from the contact piece 50, so that the switch is turned off. However, in case a wrongdoer breaks open a front frame locked with the stopper 41, with the result that the switch actuation piece and so on are broken and the switch is turned off, a display lamp in an island box comes off and an alarm sound goes off to indicate that wrongdoing has been done. Also, when a person in charge opens the stopper 41 by means of the motor during the rotation, the display lamp, an alarm, and so on are turned off.