A developer regulating member abutting against a developer carrying member carrying a mono-component developer to regulate the layer thickness of the developer on the developer carrying member has a supported portion supported by a support member, and an abutting portion abutting against the developer carrying member, the surface roughness parameters of this abutting portion satisfying the following expressions (1) to (5): 0.30.ltoreq.Sm.ltoreq.0.170 (1) Rpk.ltoreq.2.0 (2) Rp.ltoreq.5.0 (3) 0.10.ltoreq.Rvk.times.(100-Mr2)/100.ltoreq.1.30 (4) Rpk