A coupling member dismounting method for dismounting, from a drum flange mounted to an electrophotographic photosensitive drum usable with a process cartridge which is detachably mountable to a main assembly of an electrophotographic image forming apparatus, a coupling member for receiving a rotating force for rotating the electrophotographic photosensitive drum from the main assembly of the apparatus in a state in which the process cartridge is mounted to the main assembly of the apparatus, said method comprising: (i) an inclining step of inclining the coupling member relative to a rotational axis of the drum flange, wherein the coupling member includes a rotating force receiving member having, at a free end portion, a rotating force receiving portion for receiving the rotating force, a spherical portion mounted to a rear end portion of the rotating force receiving member by a pin penetration; (ii) a pin urging step of pushing the pin from one end to the other end thereof, wherein said one and the other ends of the pin are projected out of the spherical portion in a state in which the coupling member is inclined by said inclining step; wherein a regulating portion (151i; 151S, 151k) provided along an inside of the drum flange with a gap between the spherical portion and the regulating portion (151i; 151S, 151k) has a configuration nearer to a spherical surface of the free end portion than a flat plane which is perpendicular to a longitudinal direction of the electrophotographic photosensitive drum and which passes through a center of the spherical portion, and wherein said regulating portion (151i; 151S, 151k) includes a first surface extending from the regulating portion (151i; 151S, 151k) in a direction away from the coupling member toward the free end portion with respect to the longitudinal direction, and a second surface bent from the first surface extending from the regulating portion (151i; 151S, 151k) in a direction away from the coupling member toward the free end portion with respect to the longitudinal direction, (iii) a pin riding step of making a part of the pin which is further projected at the end by said pin urging step ride on the second surface; and (iv) a coupling member dismounting step of dismounting the coupling member from the drum flange by applying a force to a free end portion of the coupling member toward a fulcrum which is the portion of the pin riding on the second surface. (i) an inclining step of inclining the coupling member relative to a rotational axis of the drum flange, wherein the coupling member includes a rotating force receiving member having, at a free end portion, a rotating force receiving portion for receiving the rotating force, a spherical portion mounted to a rear end portion of the rotating force receiving member by a pin penetration; (ii) a pin urging step of pushing the pin from one end to the other end thereof, wherein said one and the other ends of the pin are projected out of the spherical portion in a state in which the coupling member is inclined by said inclining step; wherein a regulating portion (151i; 151S, 151k) provided along an inside of the drum flange with a gap between the spherical portion and the regulating portion (151i; 151S, 151k) has a configuration nearer to a spherical surface of the free end portion than a flat plane which is perpendicular to a longitudinal direction of the electrophotographic photosensitive drum and which passes through a center of the spherical portion, and wherein said regulating portion (151i; 151S, 151k) includes a first surface extending from the regulating portion (151i; 151S, 151k) in a direction away from the coupling member toward the free end portion with respect to the longitudinal direction, and a second surface bent from the first surface extending from the regulating portion (151i; 151S, 151k) in a direction away from the coupling member toward the free end portion with respect to the longitudinal direction, (iii) a pin riding step of making a part of the pin which is further projected at the end by said pin urging step ride on the second surface; and (iv) a coupling member dismounting step of dismounting the coupling member from the drum flange by applying a force to a free end portion of the coupling member toward a fulcrum which is the portion of the pin riding on the second surface.