A process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus. The process cartridge comprises an electrophotographic photosensitive drum, process means actable on said electrophotographic photosensitive drum, a first cartridge side portion-to-be-guided, a second cartridge side portion-to-be-guided, a first cartridge side portion-to-be-regulated, a second cartridge side portion-to-be-regulated, a first cartridge side portion to be positioned, and a second cartridge side portion to be positioned. The process cartridge is mounted to a main assembly with a first cartridge side portion to be positioned at a first main assembly side positioning portion by the urging force of an urging member and with the second cartridge side portion to be positioned at a second main assembly side positioning portion by the urging force of the urging member.