A developing device usable with an electrophotographic image forming apparatus, said apparatus including a driving shaft (180; 1180; 1280; 9180) rotatable by a motor and having a rotating force applying portion (182; 1182; 9182), 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, said developing device comprising: i) a developing roller for developing an electrostatic latent image formed on an electrophotographic photosensitive drum, said developing roller being rotatable about an axis; and ii) a coupling member (150; 1350; 1450; 1550; 1750; 1850; 3150; 4150; 5150; 7150; 8150; 9150; 9250; 9350; 9450; 10150; 12150; 13150; 15150) for transmitting a rotating force to said developing roller, said coupling member including, a rotating force receiving portion (150a, 150d, 150e; 1350d; 1450d; 1550d, 1550e; 3150a; 4150a; 5150a, 5150d; 7150a; 8150d, 8150e; 9150d, 9150e; 9250a, 9250e; 9350d, 9350e; 9450d, 94-50e; 10150d; 12150a, 12150d; 13150d; 15150e) engageable with the rotating force applying portion to receive a rotating force from the driving shaft, and a rotating force transmitting portion (150b, 150h; 1550h; 1450h; 3150j; 4150j; 8150h; 9150h; 12150b, 12155; 12150h; 15155) for transmitting the rotating force received through said rotating force receiving portion to said developing roller, characterised by: 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 driving shaft and in which an axis of 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 the axis of said coupling member is inclined away from the rotational force transmitting angular position in a direction opposite to said pre-engagement angular position; wherein in response to a movement of said developing device when the movable member moves in said one direction, said coupling member is opposed to and engaged with the driving shaft by moving from the pre-engagement angular position to the rotational force transmitting angular position, and wherein in response to the further movement of said developing device when the movable member makes a further movement in said one direction from a position where said coupling member is engaged with the driving shaft, said coupling member is disengaged from the driving shaft by moving from the rotational force transmitting angular position to the disengaging angular position. i) a developing roller for developing an electrostatic latent image formed on an electrophotographic photosensitive drum, said developing roller being rotatable about an axis; and ii) a coupling member (150; 1350; 1450; 1550; 1750; 1850; 3150; 4150; 5150; 7150; 8150; 9150; 9250; 9350; 9450; 10150; 12150; 13150; 15150) for transmitting a rotating force to said developing roller, said coupling member including,