To make a gap between an elastic roller part of an electrify roller and a surface of a photoreceptor drum almost constant at all times regardless of such environmental conditions as temperature and humidity.

Pressing forces F1 and F2 of pressing springs 19 which press both ends of the electrifying roller 14 respectively, are increased when the environment has low temperature and low humidity, and decreased when the environment has high temperature and high humidity. Thus, the gap between each of the inside portions of the elastic roller part 17, on which portion a tape 18 is provided, and the surface of the photoreceptor drum 5 is made substantially the same as a gap defined when the environment has normal temperature and normal humidity.