Image forming apparatus having less decrease in primary transfer efficiency of toner image

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 holding member that rotatably holds the transfer roller;
• and
• a position determining unit operable to determine a relative position between the transfer roller and the image carrier rotary body, by guiding the holding member in a direction substantially perpendicular to a running surface of the belt, and abutting a first part of the holding member and a second part of the image carrier rotary body with each other, the first part and the second part opposing each other, wherein
• when viewed in an axis direction of the transfer roller, the first part has a straight linear outline parallel to a running direction of the belt, and
• the position determination unit includes:
• a guide member having a reference surface provided in the direction substantially perpendicular to the running surface of the belt;
• a first forcing member operable to force the holding member toward the reference surface so as to be brought in contact with the reference surface;
• and
• a second forcing member operable to force the holding member toward the image carrier rotary body.

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 holding member that rotatably holds the image carrier rotary body;
• and
• a position determining unit operable to determine a relative position between the image carrier rotary body and the transfer roller, by guiding the holding member in a direction substantially perpendicular to a running surface of the belt, and abutting a first part of the holding member and a second part of the transfer roller with each other, the first part and the second part opposing each other, wherein
• when viewed in an axis direction of the image carrier rotary body, the first part has a straight linear outline parallel to a running direction of the belt, and
• the position determination unit includes:
• a guide member having a reference surface provided in the direction substantially perpendicular to the running surface of the belt;
• a first forcing member operable to force the holding member toward the reference surface so as to be brought in contact with the reference surface;
• and
• a second forcing member operable to force the holding member toward the transfer roller.