A cartridge detachably mountable to a main assembly of an image forming apparatus includes a drum unit including a photosensitive drum; a developing unit including a developing roller, a driving force receiving portion, and a development gear; a driving train for transmitting the driving force to the development gear. The developing roller is movable between a contact position and spacing position relative to the drum. The driving train includes a first driving portion connected with the driving force receiving portion and a second driving portion for transmitting the driving force toward the gear. When the developing unit is in the contact position, the first and second driving portions are connected with each other to transmit the driving force from the first driving portion to the second driving portion, and when the developing unit is in the spacing position, the first and the driving portion are not connected.