An image forming unit includes a developer bearing body that supplies a developer to an image bearing body that bears a latent image, and a developer layer forming member that forms a layer of the developer on the developer bearing body. The developer has a mean volume diameter in a range from 3.0 to 5.0 .mu.m, and a bulk density in a range from 0.26 to 0.32 g/cm.sup.3. The developer layer forming member has a curved portion having a radius of curvature smaller than or equal to 0.18 mm and constituting a developer layer forming portion.