Abstract: In one aspect of the present invention, an optical image synthesizer is adapted such that there is provided a partial mirror at the junction of two projecting axes with an angle of 45.degree. with respect to these optical axes for the purpose of projecting a composite image onto a screen. By selectively moving the partial mirror about its rotation axis into the above-mentioned angular position and out of one of the projection ranges, composed images and pre-composed are respectively projected onto the screen. Preferably, the distance between the principal points of respective lenses and the screen are equal to each other within an optical system including the lenses, the mirror and the screen. A source of illuminating light for photographs is focused by means of a cylindrical lens. Means are provided for moving the level of the partial mirror along its height. A microswitch is disposed to sense a photograph holder inserted and energize the illumination lamp only when the holder is sensed.