Developing device including regulation member with different diameters of central portion and both end portions

An image forming apparatus comprising:

• a photoconductive drum;
• and
• a developing device to supply a developing agent to an electrostatic latent image formed on the photoconductive drum to develop the electrostatic latent image, wherein the developing device comprises:
• a housing to accommodate the developing agent;
• a developing roller to convey the developing agent adhered to an outer periphery of the developing roller to an outside of the housing;
• and
• a regulation member positioned apart from the developing roller and having a circular cross-sectional shape, wherein a first diameter of a central portion of the regulation member is different from diameters of both of end portions of the regulation member, the regulation member to regulate a thickness of the developing agent adhered to the developing roller.