To efficiently and surely carry out assembling of a thin plate assembly such as a photoconductive body without damaging the thin plate.

This method comprises the steps of inserting a sharp blade having two separate tips 40a and 40b into an opening of a U-shape holder 3 at steps (1) and (2), widening the width of the opening by expanding the space between two tips 40a and 40b of the inserted blade in step (3), inserting a thin photoconductive body 4 into the widened opening in step (4), and drawing back the two tips 40a and 40b of the blade after the photoconductive body 4 has been inserted into the opening in step (5).