A method of manufacturing a rotating force transmitting part of an electrophotographic photosensitive drum for a main assembly of an electrophotographic image forming apparatus, wherein the main assembly of the electrophotographic image forming apparatus includes a driving shaft, to be driven by a motor, having a rotating force applying portion, and wherein said electrophotographic photosensitive drum is dismountable from the main assembly of the electrophotographic image forming apparatus in a direction substantially perpendicular with an axial direction of the driving shaft, said method of manufacturing said rotating force transmitting part comprises the steps of: providing said electrophotographic photosensitive drum, providing a coupling member engageable with said rotational force applying portion to receive a rotational force for rotating said electrophotographic photosensitive drum in the state in which electrophotographic photosensitive drum is mounted to said main assembly of the electrophotographic image forming apparatus, and connecting said coupling member and said electrophotographic photosensitive drum such that said coupling member is capable of taking a rotational force transmitting angular position for transmitting the rotational force for rotating said electrophotographic photosensitive drum to said electrophotographic photosensitive drum and a disengaging angular position in which said coupling member is inclined away from the axis of said electrophotographic photosensitive drum from said rotational force transmitting angular position, and that, when said electrophotographic photosensitive drum is dismounted from the main assembly of the electrophotographic image forming apparatus in a direction substantially perpendicular to the axis of said electrophotographic photosensitive drum, said coupling member is capable of moving from said rotational force transmitting angular position to said disengaging angular position. providing said electrophotographic photosensitive drum, providing a coupling member engageable with said rotational force applying portion to receive a rotational force for rotating said electrophotographic photosensitive drum in the state in which electrophotographic photosensitive drum is mounted to said main assembly of the electrophotographic image forming apparatus, and connecting said coupling member and said electrophotographic photosensitive drum such that said coupling member is capable of taking a rotational force transmitting angular position for transmitting the rotational force for rotating said electrophotographic photosensitive drum to said electrophotographic photosensitive drum and a disengaging angular position in which said coupling member is inclined away from the axis of said electrophotographic photosensitive drum from said rotational force transmitting angular position, and that, when said electrophotographic photosensitive drum is dismounted from the main assembly of the electrophotographic image forming apparatus in a direction substantially perpendicular to the axis of said electrophotographic photosensitive drum, said coupling member is capable of moving from said rotational force transmitting angular position to said disengaging angular position. that said coupling member is capable of taking a rotational force transmitting angular position for transmitting the rotational force for rotating said electrophotographic photosensitive drum to said electrophotographic photosensitive drum and a disengaging angular position in which said coupling member is inclined away from the axis of said electrophotographic photosensitive drum from said rotational force transmitting angular position, and that, when said electrophotographic photosensitive drum is dismounted from the main assembly of the electrophotographic image forming apparatus in a direction substantially perpendicular to the axis of said electrophotographic photosensitive drum, said coupling member is capable of moving from said rotational force transmitting angular position to said disengaging angular position.