the rotational center of the developing roller 26 and the separating piece 82 is positioned beneath the protrusion 232 the separating member 80 separates from the protrusion 232 when the edge of the separating piece 82 having the shortest distance to the rotational shaft 81 opposes the protrusion 232 and pushes up the protrusion 232 against the urging force of the pressing member 70 when the edge of the separating piece 82 having the longest distance from the rotational shaft 81 opposes the protrusion 232 next the effects of using the laser printer 1 having the construction described above will be described the cases 23 in the laser printer 1 have a high stiffness with respect to a force applied along the end face 23 a further the protrusions 231 and protrusions 232 are provided on the upper ends of the end faces 23 a in the laser printer 1 of the preferred embodiment therefore instead of pressing the case 23 as in the conventional laser printers the laser printer 1 of the preferred embodiment can apply pressing and separating forces via the protrusions 231 and protrusions 232 without directly applying a force to the case 23 for separating the developing roller 26 from the photosensitive drum 30 hence since the pressing force and separating force are not applied to the case 23 at single points it is unnecessary to increase the stiffness of the case 23 moreover it is.