A toner receiving member, which is open upward, is provided at a position vertically below a lower end of a contact surface between a side seal member and a developing roller. The toner receiving member can receive and store toner which has leaked. In addition, when a developing cartridge is removed from a main body casing and then placed on a horizontal surface such as a desktop, a front wall, which serves as a bottom surface of the toner receiving member, faces upward. Toner collected in the toner receiving member may be prevented from leaking.