PURPOSE: To make effective use of emission luminous fluxes by providing the contacts sufficiently contacting the switch mechanism of a light emitting device.

CONSTITUTION: A spring contact piece 1b is carried on the T-shaped member 7 of the light-quantity-responding electro-mechanic transducer 9 in a photometric circuit. At the using of the light emitting device, the scanning edge part of the member 7 formed at one end of shutter blades 1, 2 along with the shutter blade operation is abutted on the member 7 to effect a trigger function for the purpose of abutting a contact piece 9b on a counter provided stationary contact piece 10b, so that the switch is closed before the peak of the shutter waveform reaches. After this, the contact time of the switch contacts is sufficiently maintained.