Image forming apparatus

An image forming apparatus comprising:

• an image forming portion configured to form toner images;
• a rotatable intermediary transfer belt onto which the toner images formed by said image forming portion are transferred;
• a plurality of stretching rollers stretching said intermediary transfer belt and including an inner roller and an upstream roller provided adjacent to said inner roller on a side upstream of said inner roller with respect to a rotational direction of said intermediary transfer belt;
• an outer roller contacting an outer peripheral surface of said intermediary transfer belt and configured to form a transfer nip, where the toner images are transferred from said intermediary transfer belt onto a recording material, by nipping said intermediary transfer belt between said outer roller and said inner roller;
• a moving mechanism capable of moving a position of said inner roller between a first position where an offset amount X is a first offset amount X1 and a second position where the offset amount X is a second offset amount X2, which is greater than the first offset amount X1, wherein in a cross-section perpendicular to a rotational axis direction of said inner roller, an external common tangential line between said inner roller and said upstream roller on a side where said intermediary transfer belt is stretched by these rollers is a reference line L1, a rectilinear line passing through a rotation center of said inner roller and perpendicular to the reference line L1 is an inner roller center line L2, a rectilinear line passing through a rotation center of said outer roller and perpendicular to the reference line L1 is an outer roller center line L3, and a distance between the inner roller center line L2 and the outer roller center line L3 is the offset amount X, which is a positive value when the outer roller center line L3 is positioned upstream of the inner roller center line L2 with respect to the rotational direction of said intermediary transfer belt;
• and
• a controller configured to control said moving mechanism,
• wherein said controller is capable of executing an operation in a first mode and an operation in a second mode, in which a continuous image forming job for transferring toner images onto a plurality of recording materials including a first recording material and a second recording material subsequent to the first recording material is executed,
• wherein in the first mode, when the toner images are transferred onto the first recording material having a second basis weight, the position of said inner roller is the second position, and when the toner images are transferred onto the second recording material having a first basis weight greater than the second basis weight, the position of said inner roller is the second position, and
• wherein in the second mode, when the toner images are transferred onto the first recording material having the second basis weight, the position of said inner roller is the second position, and when the toner images are transferred onto the second recording material having the first basis weight greater than the second basis weight, the position of said inner roller is the first position.