Image forming apparatus that ensures highly accurate positioning on photoreceptor drum of primary transfer roller

An image forming apparatus comprising:

• an apparatus main body;
• a plurality of photoreceptor drums each rotatably driven around shaft centers extending in a first direction, the photoreceptor drums forming electrostatic latent images on circumference surfaces, the photoreceptor drums being arranged in a second direction with intervals, the second direction being perpendicular to the first direction;
• a plurality of developing devices opposed to the plurality of respective photoreceptor drums, the developing devices supplying toner to the circumference surfaces on the photoreceptor drums to form toner images on the circumference surfaces;
• a frame that supports the plurality of photoreceptor drums and the plurality of developing devices, the frame being removably attachable to the apparatus main body along the second direction, the frame being positioned to and secured to the apparatus main body;
• an intermediate transfer unit mounted to the frame to be removably attachable to the apparatus main body integrated with the frame, the intermediate transfer unit including:
• an intermediate transfer belt running to extend along the second direction, the intermediate transfer belt being opposed to the plurality of photoreceptor drums and circularly driven, the toner images being transferred from the plurality of photoreceptor drums to the intermediate transfer belt;
• a first roller supporting the intermediate transfer belt at a distal end side in a mounting direction of the frame with respect to the apparatus main body;
• a second roller supporting the intermediate transfer belt at a rear end side in the mounting direction;
• and
• a plurality of primary transfer rollers each opposed to the photoreceptor drums across the intermediate transfer belt at an inner peripheral portion of the intermediate transfer belt, the primary transfer rollers causing the toner images to be transferred from the photoreceptor drums to the intermediate transfer belt;
• a secondary transfer roller arranged in the apparatus main body to be opposed to the first roller across the intermediate transfer belt, the secondary transfer roller forming a secondary transfer nip portion with the first roller where the toner images are transferred to a sheet;
• first positioning portions arranged at the intermediate transfer unit and the frame, the first positioning portions positioning the intermediate transfer unit in the second direction inside the apparatus main body;
• and
• second positioning portions arranged at the intermediate transfer unit and the apparatus main body, the second positioning portions positioning a distal end side in the mounting direction of the intermediate transfer unit in a third direction inside the apparatus main body, the third direction intersecting with the first direction and the second direction.