Developing device, process cartridge, and image forming apparatus

A regulation member includes an opposed surface and a contact surface in a portion corresponding to an image forming area. The opposed surface is opposed to a developer bearing member. The contact surface protrudes from the opposed surface and has a height different from that of the opposed surface. An end seal seals a gap between a frame body, the developer bearing member, and the regulation member. The regulation member further includes an area not having the contact surface between the image forming area and a sealing area in which the regulation member and the end seal overlap. In the sealing area, a step between the opposed surface and the contact surface has a height of greater than or equal to 0 mm and not greater than 0.10 mm.