A developing device usable with an electrophotographic image forming apparatus, said apparatus including an electrophotographic photosensitive drum, a driving shaft rotatable by a motor and having a rotating force applying portion, and a movable member, said developing device being mountable to the movable member, and said developing device being movable in a direction substantially perpendicular to an axial direction of the driving shaft in response to movement of the movable member in one direction with said developing device mounted to the movable member, wherein said driving shaft is not movable in a direction perpendicular to an axis thereof, said developing device comprising: i) a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum, said developing roller being rotatable about an axis, wherein said developing roller is contacted to and separated from said electrophotographic photosensitive drum in response to movement of said movable member; and ii) a coupling member for transmitting a rotating force to said developing roller, said coupling member including, a rotating force receiving portion engageable with the rotating force applying portion to receive a rotating force from the driving shaft, and a rotating force transmitting portion for transmitting the rotating force received through said rotating force receiving portion to said developing roller, said coupling member being capable of taking a rotational force transmitting angular position for transmitting the rotational force for rotating said developing roller to said developing roller, a pre-engagement angular position which is taken before said coupling member is engaged with the rotating force applying portion and in which said coupling member is inclined away from said rotational force transmitting angular position, and a disengaging angular position which is taken for said coupling member to disengage from the driving shaft and in which said coupling member is inclined away from the rotational force transmitting angular position in a direction opposite to said pre-engagement angular position, wherein said developing device is adapted such that in response to a movement of said developing device when the movable member moves in said one direction, said coupling member moves from the pre-engagement angular position to the rotational force transmitting angular position, and wherein when the movable member makes a further movement in said one direction, in response to the further movement, said coupling member is moved from said rotational force transmitting angular position to said disengaging angular position to disengage said coupling member from said driving shaft, and wherein said developing device is adapted such that said developing roller is contacted to said electrophotographic photosensitive drum in response to the movement of said developing device in a state that said developing roller is being rotated through engagement between said coupling member and said rotating force applying portion. i) a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum, said developing roller being rotatable about an axis, wherein said developing roller is contacted to and separated from said electrophotographic photosensitive drum in response to movement of said movable member; and ii) a coupling member for transmitting a rotating force to said developing roller, said coupling member including, a rotating force receiving portion engageable with the rotating force applying portion to receive a rotating force from the driving shaft, and a rotating force transmitting portion for transmitting the rotating force received through said rotating force receiving portion to said developing roller, said coupling member being capable of taking a rotational force transmitting angular position for transmitting the rotational force for rotating said developing roller to said developing roller, a pre-engagement angular position which is taken before said coupling member is engaged with the rotating force applying portion and in which said coupling member is inclined away from said rotational force transmitting angular position, and a disengaging angular position which is taken for said coupling member to disengage from the driving shaft and in which said coupling member is inclined away from the rotational force transmitting angular position in a direction opposite to said pre-engagement angular position,