To keep the developing gap of a developing roller relative to a photoreceptor drum uniform without using an extra pressing member separately.

A developing device comprises: the photoreceptor drum; the developing roller; a developer supply roller; a first support which supports the photoreceptor drum so that the drum freely rotates; an idle gear which is disposed such that the center of the photoreceptor drum, the center of the development roller, and the center of the idle gear form a triangle, and which transmits rotating force of the developing roller to the developer supply roller; a second support which supports the developing roller so that it freely rotates; and a positioning member which is freely turnably supported by the first support at one end and positions the developing roller relative to the photoreceptor drum. In the developing device, the turning point of the positioning member present on a line (G) connecting the centers of the idle gear and developing roller.