In a developing device, a developing roller has a circumferential surface and an axial end portion. A thickness-regulating blade includes a pressing part protruding to contact the circumferential surface. A first sealing member is provided between a housing and the axial end portion, and includes a first layer; and a second layer. The first layer has a first layer surface disposed to contact the circumferential surface. The second layer supports the first layer and has a protruding part protruding inward of the first layer in an axial direction of the developing roller and having a second layer surface opposing the circumferential surface. The housing has a wall part disposed between the pressing part and the protruding part in the rotating direction of the developing roller. The wall part has an opposing surface opposing the circumferential surface. A lubricant is applied to the first layer surface and the second layer surface.