PURPOSE: To prevent malfunction due to a noise from being generated by providing three switching elements: the element to operate a relay by a trigger signal, a thyristor-connected element, and the element to impress a voltage on the element and a light emitting element by the operation of the relay.

CONSTITUTION: In case of adding an ordinary trigger signal, a first switching(Sw) element 3 is turned ON, and the relay 2 is operated, and the contact 2a of the relay makes. Then, a third Sw element 5 is turned ON, and an operating voltage is applied on the light emitting element 1 and a second Sw element 4. In other words, the trigger signal is latched, and the relay is operated, and also, light emission display is performed by the light emitting element 1. When a noise is inputted, the element is turned OFF before the relay 2 is operated since pulse width is small even when the element 3 is turned ON, and the contact 2a keeps a break state, and the element 4 is not turned ON, and the element 3 turned ON once is turned OFF, thereby, it is possible to surely prevent the malfunction from being generated.