Patent ID: 8285181

Claim:
An image forming apparatus that transfers a toner image from an image carrier rotary body provided outside an outer circumferential surface of a running belt onto the outer circumferential surface with use of a transfer roller that contacts with an inner surface of the belt, the image forming apparatus comprising: a first holding member that rotatably holds the image carrier rotary body; a second holding member that rotatably holds the transfer roller; and a position determining unit operable to determine a relative position between the image carrier rotary body and the transfer roller, by guiding one of the first and second holding members in a direction substantially perpendicular to a running surface of the belt, and abutting a first part of the first holding member and a second part of the second holding member with each other, the first part and the second part opposing each other, wherein when viewed in an axis direction of the transfer roller, one of the first and second parts has a straight linear outline parallel to a running direction of the belt, and the other of the first and second parts has a convex curved outline, and the position determining unit includes: a guide member having a reference surface extending in the direction substantially perpendicular to the running surface of the belt; a first forcing member operable to force, toward the reference surface, one of the first and second holding members to be guided, so as to be brought in contact with the reference surface; and a second forcing member operable to force, toward the other holding member, the one holding member to be guided.