Abstract: A combination of a plate for exposure, such as a printed circuit board, having a pair of photosensitive layers formed on its opposite surfaces, and a pair of transparent frame plates between which the plate for exposure can be sandwiched, and which are each provided with a mask on its surface facing the plate for exposure. The plate for exposure is formed with a pair of apertures adjacent to each of a pair of opposite edges thereof. Each of the frame plates is provided adjacent to each of a pair of opposite edges thereof with a pin facing one of the apertures and a recess facing the other aperture. The pin on one of the frame plates faces the recess in the other frame plate. The pins are so sized and shaped that they can be easily fitted in, and removed from the apertures, and can hold the frame plates against displacement relative to the plate for exposure when fitted in the apertures.