Image forming apparatus having detachable image bearing and transfer belt mechanisms

An image forming apparatus comprising:

• an image bearing mechanism that is attachable to and detachable from an apparatus body in a first direction and that supports a plurality of image bearing members, each image bearing member having a surface onto which an image is formed while the image bearing member rotates;
• a transfer belt mechanism including a transfer belt onto which the images on the plurality of image bearing members are transferred while the image bearing members rotate, the transfer belt mechanism being attachable to and detachable from the apparatus body in a second direction different from the first direction, and
• wherein the regulating unit is a protrusion provided in the transfer belt mechanism, the protrusion abutting on the image bearing mechanism when the transfer belt mechanism attached to the apparatus body is to be detached from the apparatus body.