PURPOSE: To inhibit releasing when abnormality occurs in the changeover of a photographic picture frame by providing detecting mechanisms in both of a photographic picture frame region shielding,member and a display means in a photographic picture frame region in a finder.

CONSTITUTION: Detecting terminals 1g and 1h and 1i and 1j are connected by light shielding plates 2 and 3 respectively to electrically detect the changeover of a picture size. Moreover, a visual field mask 20 pushed upward by a rotary lever moving linked with the plates 2 and 3 is slid downward by a press spring 25 by the movement of the rotary lever, so that a mask armature 23a is depressed and brought into contact with a mask armature 23b, to electrically detect the fact that the top end part 20b of the visual field mask shields the upper part of the visual field frame 24 from the light. When a malfunction occurs even in a place of the plates and 3 or the masks 20 and 21, the main switch SW of a camera is turned on and the abnormality in the changeover of the picture size is judged because the signals of the detections of the positions of the plates 2 and 3 and the masks 20 and 21 do not coincide.