PURPOSE: Not to cause the lighting circuit of the light source for use in data photographing to respond to a false signal by providing a filter circuit consisting of capacitor which absorbs the influence of chattering is series with a switch which starts the data photography.

CONSTITUTION: Instruction for data photographing issues with closing of synchro- switch S4 of the camera. Trigger circuit of SC of SCR comprises parallel circuit of R6 and C4 connected to one end of S4 and series circuit of C3 and R7 connected between two terminals of D4, and the connecting point of C3 with R7 is coupled to gate of SC. Time constant of R6 and C4 is set sufficiently larger than the period of chattering of S4, and it never happens that the potential changes vibratorily at the point P1, although chattering takes place when S4 is closed. The potential at P1 approaches to the positive potential almost instantly by closing of S4, but no response occurs regardless of chattering. In addition, L1 is lamp of the light source for data photography.