Image forming apparatus

An image forming apparatus comprising:

• an apparatus main assembly;
• a unit detachably mountable to said apparatus main assembly;
• a first coupling, provided on said apparatus main assembly, for being rotated by power from a driving source;
• and
• a second coupling, provided on said unit, for being rotated by engaging with said first coupling,
• wherein one of said first coupling and said second coupling has a recessed shape and the other of said first coupling and said second coupling has a projected shape, wherein at least one of an outer peripheral surface of the projected-shape coupling and an inner peripheral surface of the recessed-shape coupling has an inclined surface,
• wherein at least one of said first coupling and said second coupling is retractable toward a direction parallel to a rotation shaft thereof, and
• wherein said image forming apparatus has a structure such that a rotation axis of said second coupling is movable relative to a rotation axis of said first coupling in a disengaging direction of said unit by a force exerted in the disengaging direction of said unit when said unit is pulled out from said apparatus main assembly in the disengaging direction perpendicular to the rotation axis of said first coupling and then by contact of the inclined surface and by such relative movement of the rotation axes, at least one of said first coupling and said second coupling starts retracting along the inclined surface in the direction parallel to the rotation axis from a state in which said first and second couplings are engaged to be rotated.