The invention concerns a pressing portion of a layer thickness-regulating blade for pressing toner on a developing roller and forming a thin layer of toner is formed from a silicone rubber. The pressing force of the pressing portion is set to 15-30 gf/cm. Since toner is pressed against the developing roller by the portion made of the silicone rubber having a high electrical charging characteristic, toner is sufficiently electrically charged. Furthermore, since the pressing force or pressure of the pressing portion is very weak, the abrasion of the silicone rubber-made portion is reduced.