To prevent the on/off switching of the power source switch of a stroboscope from being interfered by a shock such as dropping.

The power source switch 30 consisting of an elastic contact piece 30a and a fixed contact piece 30b is provided on the front surface of a stroboscopic circuit board 26. A guide plate 35 and an operation plate 42 are assembled on the front surface of the circuit board 26, and an operation button 6 provided on the plate 42 is projected from the aperture 21a of a front cover to the front surface side of the front cover. A switch pressing pin 44 is protrusively provided at a position where it does not face to the aperture 21a on the back of the plate 42, and made to face to the contact piece 30a through the through-hole 39a of a guide plate 35. When the button 6 is operated to be pushed in against the energizing of a recovery spring 38, the pin 44 is moved to the back side together with the plate 42 and bends the piece 30a with its tip. The tip of the armature 30a comes into contact with contact piece 30b so as to turn on the switch 30.