Tandem type photosensitive unit and image forming apparatus

An image forming apparatus comprising:

• an apparatus body;
• and
• a tandem type photosensitive unit configured to be detachably mounted in the apparatus body, wherein
• the tandem type photosensitive unit comprises:
• a plurality of photosensitive drums arranged in parallel with one another;
• a first structure member having a side surface extending in an arrangement direction of the photosensitive drums as viewed from an axial direction of the photosensitive drums, the first structure member being configured to position and retain each of the plurality of photosensitive drums;
• and
• a second structure member having a side surface extending in the arrangement direction as viewed from the axial direction, the second structure member being configured to retain a plurality of developer cartridges provided correspondingly to the photosensitive drums respectively,
• wherein the first structure member is fixed to the second structure member on one side of the second structure member, and mounted with a clearance on the other side of the second structure member relative to the arrangement direction, and
• wherein the other side of the second structure member is configured to provide a clearance which accounts for a difference in the expansion or contraction of first structure member relative to the second structure member.