A developing cartridge has a housing that accommodates developer therein. Rotatably mounted in the housing is a developing roller. The housing has side seals provided at each end of the developing roller that oppose the circumferential ends of the developing roller. The developing roller itself is divided into a seal region, a side-end region and a center region. A portion of the seal region and the side-end region found at each end of the developing roller with the seal region portions being at the ends of the roller and the side end region portions being between the seal region portions and the center region. Opposing the developing roller is a toner thickness regulating blade having a presser portion. The presser portion has a discontinuous cross-section such that a greater portion of the presser member contacts the developer roller in each portion of the side-end region then contacts the developer roller in the center region. As a result, a greater pressure is applied between the presser portion and the developer roller at the side-end region thereby resulting in less toner being applied to the developing roller to be carried to a photosensitive member. To further the minimize the amount of toner applied to the developing roller, the roughness in the side end region of the developing roller is smaller than the roughness in the center region and the hardness in the side end region of the developing roller is greater than the hardness in the center region. This combination of factors prevents toner from leaking from the housing at the ends of the developing rollers.