PURPOSE: To prevent discoloration and fading of an image due to aging, by processing a diazo type photographic paper imagewise exposed and developed, with an ag. tannin soln. of specified concn.

CONSTITUTION: A photosensitive soln. consisting essentially of a diazonium salt is coated on paper and dried to obtain diazo type photosensitive paper 1. A sheet of the paper 1 is underlaid beneath an original 2, introduced into a copying machine 4, moved while pressed into contact with the circumference of a photosensitive drum 8 consisting of UV lamps 6 and a galss cylinder 7, and the diazonium salt is photodecomposed. The original 2 is separated, the paper 1 is indtroduced into a developing tank 10 to execute development, passed through a tank 11 containing a 0.05W2%ag. tannin soln., dehydrated by squeezing with rolls, and then, discharged from the machine 4. As a tannin treatment process, the ag. tannin soln. may be coated or atomized on the photographic paper in place of dipping.