An electrophotographic image forming apparatus detachably mounts a process cartridge including an electrophotographic photosensitive drum. The apparatus includes a frame, a door, and a tray carrying the cartridge. The tray is movable among a first position inside the frame when the door is closed and the drum forms a latent image, a second position when the door is open and the tray protrudes from the frame to permit cartridge mounting and demounting, and a third position between the first and second positions where the tray is movable to the first position with closing of the door. Also, a regulating member moves between a regulating position regulating movement of the door from an opening position to a position where the tray is beyond the third position, and a permitting position permitting movement of the door from the opening to the closing position when the tray is at the third position.