To prevent the deterioration of a developing roller or adverse influence exerted on image formation because of installing toner sealing structure on the developing roller.

A sealing pad 11 is disposed between the opposite side of the developing roller 4 to the surface of the roller 4 opposed to a photoreceptor drum 1 and the inner wall of a developing case 3, and toner Ta is made to intervene as a lubricant in a gap abutting on the roller 4 on the pad 11. By making the toner Ta intervene as the lubricant, friction and frictional resistance between the pad 11 and the roller 4 reduced even though the pad 11 is made to abut on the roller 4 for the purpose of toner sealing in the conventional manner, so that frictional heat and the increase of driving torque are restrained, the roller 4 is prevented from being damaged, and operation is made stable.