A cartridge comprising: a photosensitive drum; a casing having a first end portion and a second end portion opposite from the first end portion in an axial direction of the photosensitive drum, the casing rotatably supporting the photosensitive drum; and a coupling operatively connected to the photosensitive drum so as to be capable of transmitting a driving force toward the photosensitive drum, wherein the coupling includes: a first wall, a second wall provided inside the first wall in a radial direction of the coupling, a groove portion defined by the first wall and the second wall, a recessed portion provided in the second wall, and an inclined portion adjacent the recessed portion, wherein at least a part of the inclined portion is more remote from an axis of the coupling than the recessed portion, wherein one of the sides of the recessed portion in a circumferential direction of the coupling is opened, and on the other side of the recessed portion in the circumferential direction, at lease a part of the inclined portion is provided, and wherein the inclined portion is inclined so as to go away from the second end portion of the casing in the axial direction of the photosensitive drum as goes away from the recessed portion in the circumferential direction, characterized in that at least a part of the recessed portion and at least a part of the inclined portion are inside the groove portion. a photosensitive drum; a casing having a first end portion and a second end portion opposite from the first end portion in an axial direction of the photosensitive drum, the casing rotatably supporting the photosensitive drum; and a coupling operatively connected to the photosensitive drum so as to be capable of transmitting a driving force toward the photosensitive drum, wherein the coupling includes: a first wall, a second wall provided inside the first wall in a radial direction of the coupling, a groove portion defined by the first wall and the second wall, a recessed portion provided in the second wall, and an inclined portion adjacent the recessed portion, wherein at least a part of the inclined portion is more remote from an axis of the coupling than the recessed portion, wherein one of the sides of the recessed portion in a circumferential direction of the coupling is opened, and on the other side of the recessed portion in the circumferential direction, at lease a part of the inclined portion is provided, and wherein the inclined portion is inclined so as to go away from the second end portion of the casing in the axial direction of the photosensitive drum as goes away from the recessed portion in the circumferential direction, a first wall, a second wall provided inside the first wall in a radial direction of the coupling, a groove portion defined by the first wall and the second wall, a recessed portion provided in the second wall, and an inclined portion adjacent the recessed portion, wherein at least a part of the inclined portion is more remote from an axis of the coupling than the recessed portion, wherein one of the sides of the recessed portion in a circumferential direction of the coupling is opened, and on the other side of the recessed portion in the circumferential direction, at lease a part of the inclined portion is provided, and wherein the inclined portion is inclined so as to go away from the second end portion of the casing in the axial direction of the photosensitive drum as goes away from the recessed portion in the circumferential direction,