A developing roller that supplies developing agent onto an electrostatic latent image on an image carrier, and a layer regulating blade that pressure contacts the developing roller and regulates a uniform layer thickness of the developing agent that is supplied to the developing roller are arranged, and an elastic resin coat layer whose thickness t is 10×a≦t≦300 [&mgr;m] is coated on the surface of the layer regulating blade, when the surface of the above developing roller is formed of a metallic material whose surface roughness Rz is a [&mgr;m], and the layer regulating blade is made of a metallic material. While, the developing roller that supplies developing agent onto the electrostatic latent image on an image supporting material, and the layer regulating blade that pressure contacts the developing roller and regulates a uniform layer thickness of the developing agent that is supplied to the developing roller are arranged, and the surface of the developing roller is made of brass, and the layer regulating blade is formed of stainless steel, and the pressing force of the layer regulating blade to the developing roller is 70-100[gf/cm].