The invention relates to a developing device removable from an imaging device, especially a developing box, comprising: a box body containing powder storehouse and developing device and side end cover, a developer mixing device located in the powder storehouse, a powder supply roller to supply developer to developing roller, a developing roller to develop static latent image on photosensitive body, and a limiting piece to control thickness of developer layer on the developing roller, where there is a drive bay with power receiving mouths in each roller-end gear set outside the side end cover, and it is characterized in that: the casing of the box body in the direction vertical to the side end cover is of an arc shape, the box body is integrated with the side end cover; the number of side end covers is one or two; the box body and the side end cover are connected by lockpin, locker or bolt; the number of power receiving mouths is two or more; it saves manpower, material resources and financial resources, and besides, its appearance is more beautiful; its universality is improved.