A cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, said main assembly including a first coupling member which is rotatable about a first axis and which has a first edge line provided at a free end portion with respect to a direction of the first axis, said cartridge comprising: a second coupling member which is rotatable about a second axis and which has a second edge line provided at a free end portion with respect to a direction of the second axis, said second coupling member being engageable with the first coupling member to receive a driving force form the first coupling member; and a rotatable member rotatable by the driving force received by said second coupling member; wherein when the first edge line and the second edge line are contacted to each other at a point of contact before the first coupling member and said second coupling member are engaged with each other, upon mounting said cartridge to the main assembly of the apparatus so as to bring said second coupling member close to the first coupling member in a state in which the first axis and the second axis are substantially aligned with a common phantom line, (i) lines (51g, 42g) being virtual extensions of the first edge line and the second edge line on a first phantom plane including the phantom line are crossed with each other, and (ii) line segments (51h, 42h) being projections of the first edge line and the second edge line projected on a second phantom plane perpendicular to the phantom line are crossed with each other, characterised in that: both of a normal line of the line segment of the first edge line and a normal line of the line segment of the second edge line at the point of contact do not pass through the phantom line. a second coupling member which is rotatable about a second axis and which has a second edge line provided at a free end portion with respect to a direction of the second axis, said second coupling member being engageable with the first coupling member to receive a driving force form the first coupling member; and a rotatable member rotatable by the driving force received by said second coupling member; wherein when the first edge line and the second edge line are contacted to each other at a point of contact before the first coupling member and said second coupling member are engaged with each other, upon mounting said cartridge to the main assembly of the apparatus so as to bring said second coupling member close to the first coupling member in a state in which the first axis and the second axis are substantially aligned with a common phantom line, (i) lines (51g, 42g) being virtual extensions of the first edge line and the second edge line on a first phantom plane including the phantom line are crossed with each other, and (ii) line segments (51h, 42h) being projections of the first edge line and the second edge line projected on a second phantom plane perpendicular to the phantom line are crossed with each other, characterised in that: both of a normal line of the line segment of the first edge line and a normal line of the line segment of the second edge line at the point of contact do not pass through the phantom line. (i) lines (51g, 42g) being virtual extensions of the first edge line and the second edge line on a first phantom plane including the phantom line are crossed with each other, and (ii) line segments (51h, 42h) being projections of the first edge line and the second edge line projected on a second phantom plane perpendicular to the phantom line are crossed with each other, characterised in that: both of a normal line of the line segment of the first edge line and a normal line of the line segment of the second edge line at the point of contact do not pass through the phantom line.