PURPOSE:To enhance working efficiency and printing accuracy, in performing the photosensitive baking of a positive image classified by color to the screen provided to an original under tension and mounting the original to the mount frame of a printing press, by respectively engaging locating projections with locating holes. CONSTITUTION:An original 1 is placed on a flat plate 8 and a transparent film 3 is superposed thereon and punched pieces 4 classified by color are adhered to the film 3 in matching relation to the same color parts of the original to successively form a plurality of positive images 5 classified by color. At this time, two locating projections 11 provide on the flat plate 8 in a protruded state so as to provided an interval therebetween are tightly engaged with the locating holes 12, 13 formed to the transparent film to perform positional determination. The positive images 5 classified by color are placed on the glass plate of a baking machine and an original plate having a screen coated with a photosensitive agent provided thereto under tension is superposed thereon to perform photosensitive baking. At this time, the glass plate and the original plate are also tightly connected in the same way by two locating projections and two locating holes and, further, same positional determination is also performed when the original is mounted to the mount frame of a printing press.