Image forming apparatus with a stopper member and an urging member

An image forming apparatus comprising:

• an apparatus body;
• a photosensitive member unit including a photosensitive member on which an electrostatic latent image is formed, and configured to be attachable to and detachable from the apparatus body and positioned relative to the apparatus body;
• a developing unit including a developer carrier for bearing and carrying a developer for developing the electrostatic latent image formed on the photosensitive member, and configured to be attachable to and detachable from the apparatus body and positioned relative to the photosensitive member unit attached to the apparatus body;
• a pressing member configured to be movable between a first position for pressing the developing unit toward the photosensitive member unit and a second position for releasing application of pressure to the developing unit;
• a stopper member configured to be movable between a regulating position for preventing the pressing member from moving from the second position to the first position and a retracting position for permitting the pressing member to move from the second position to the first position, the retracting position being retracted from the regulating position;
• and
• an urging member configured to urge the stopper member,
• wherein, in a case where the developing unit is attached to the apparatus body and the photosensitive member unit is also attached to the apparatus body, the stopper member urged by the urging member is at the retracting position, and
• wherein, in a case where the developing unit is attached to the apparatus body and the photosensitive member unit is not attached to the apparatus body, the stopper member urged by the urging member is at the regulating position.