Patent ID: 8577255

Claim:
An image forming apparatus comprising: a main body; an endless belt; and a drum unit configured to be detachably mounted on the main body, the drum unit configured to be inserted in a mounting direction to mount on the main body, the drum unit having a first end and a second end disposed downstream of the first end in the mounting direction, the drum unit configured to support a plurality of photosensitive drums including a black photosensitive drum and color photosensitive drums, the black photosensitive drum having a first axis extending in an axial direction perpendicular to the mounting direction, each of the color photosensitive drums having a second axis extending in a direction parallel to the axial direction, the black and color photosensitive drums being arranged in the mounting direction, the black photosensitive drum being disposed at a position near the first end, the second end being pivotable about the first axis to be movable between an initial position and a pivot position, wherein the black and color photosensitive drums contact the endless belt when the drum unit is disposed in the initial position, wherein the black photosensitive drum contacts the endless belt and the color photosensitive drums are separated from the endless belt when the drum unit is disposed in the pivot position, wherein the main body comprises a reference part configured to adjust a position of the drum unit in the main body, wherein the reference part is disposed downstream of the first axis in the mounting direction when the black photosensitive drum is supported in the drum unit and the drum unit is mounted in the main body, wherein the second end contacts the reference part when the plurality of photosensitive drums are in contact with the endless belt, and wherein the second end is separated from the reference part when the drum unit is disposed in the pivot position.