A coupling member drum unit for a cartridge includes a cylindrical photosensitive drum having an axis L1 and a coupling member operatively connected to the photosensitive drum. The coupling member includes a drum flange provided at an end of the photosensitive drum, with a part of the drum flange being positioned inside of the photosensitive drum, and a connecting part operatively connected to the drum flange. The connecting part includes a cap positioned adjacent to the drum flange, an arm portion extending from the cap in a direction of the axis L1, and a projection projecting from the arm portion in a direction perpendicular to the axis L1, with the projection being movable between a first position and a second position, and with an end of the projection being closer to the axis L1 in the first position than in the second position.