A developing device used with an image forming apparatus has a driving shaft with a rotating force applying portion, and a movable member on which the developing device is mountable. The developing device includes a developing roller and a coupling member for transmitting a rotating force to the developing roller. The coupling member includes a rotating force receiving portion and a rotating force transmitting portion for transmitting a force received through the rotating force receiving portion to the developing roller. The coupling member can be in a rotational force transmitting angular position, a pre-engagement angular position, and a disengaging angular position. In response to movement of the movable member the coupling member moves from the pre-engagement angular position to the rotational force transmitting angular position, and by moving from the rotational force transmitting angular position to the disengaging angular position the coupling member is disengaged from the driving shaft.