An electrophotographic image forming apparatus to which a process cartridge is detachably mountable, the process cartridge can be positioned with high accuracy in a simple construction in an apparatus main body. The process cartridge is put on a cartridge tray, and the process cartridge is replaced by a front access. Furthermore, the process cartridge is moved in conjunction with opening/closing operations of a door member so that a photosensitive drum and a transfer belt are brought in contact with each other.