A developing cartridge detachably mountable to an image forming apparatus main body having main body side guide portions and a cartridge mounting portion, including: a developer containing portion; a developing roller for developing a latent image formed on a photosensitive member with developer; first cartridge side guide portions provided at one end and the other end in a longitudinal direction of the roller, for engaging with the main body side guide portions to regulate a movement locus of the cartridge when the cartridge is mounted to the main body; and protruding portions provided at one end and the other end in the longitudinal direction, wherein the cartridge is mounted to the main body in a mounting direction orthogonal to the longitudinal direction with the roller being a leading edge, and the protruding portions protrude on a downstream side further than the roller in the mounting direction.