Image forming apparatus

An image forming apparatus, comprising:

• a housing;
• a drum unit including a photosensitive drum assembly rotatable about a rotation axis direction and a drum frame supporting the photosensitive drum assembly, the drum unit being attachable to and detachable from the housing;
• an exposure head including a plurality of light emitters aligning along the rotation axis direction, a lens array through which light from the plurality of light emitters is focused on a surface of the photosensitive drum assembly, a head frame supporting the plurality of light emitters and the lens array, and a contact member defining a distance between the lens array and the photosensitive drum assembly in an optical axis direction by contacting the drum unit, the optical axis direction being a direction of an axis of the light from the lens array, the exposure head being movable between an exposable position, at which the photosensitive drum assembly is exposable to the light from the plurality of light emitters, and a retracted position, at which the exposure head is retracted from the exposable position;
• and
• a holder supporting the head frame,
• wherein the drum unit includes a contact face, the contact face being configured to define the distance between the lens array and the photosensitive drum assembly by contacting the contact member in the exposure head located at the exposable position,
• wherein the holder includes a supporting portion supporting the head frame on an inner side with respect to the contact face in the rotation axis direction, and
• wherein the drum unit is attachable to or detachable from the housing under a condition where the exposure head is located at the retracted position.