An image forming apparatus cartridge includes a casing, a developer roller having an axis L1, and coupling member having an axis L2. The coupling member includes (i) a first end portion operatively connected with the developer roller, (ii) a second end portion having an outermost surface, (iii) an axle portion connecting the first end portion and the second end portion to each other, and (iv) at least one projection extending from the second end portion. For at least part of the outermost surface of the second end portion, a maximum distance from the axis L2 to the outermost surface along a line perpendicular to the axis L2 increases as the distance along the axis L2 from the axle portion increases.