A process cartridge is detachably mountable to a main assembly of an image forming apparatus. The process cartridge includes an image bearing member, a cleaning member for removing a developer from the image bearing member, a frame provided with an opening, and a developer accommodating portion for accommodating the developer which was removed by the cleaning member and passed through the opening. A sheet member is also provided, contacting the image bearing member, for preventing the developer from leaking out of the developer accommodating portion. A supporting portion is provided to the frame, for supporting the sheet member. A reinforcing portion, provided to the frame, connecting one end side portion of the frame located upstream of the opening with the other end side portion of the frame located downstream of the opening, with respect to a rotational direction of the image bearing member.