| 摘要 |
An image forming apparatus includes a rotatable belt member; a stretching roller for stretching the belt member; a plurality of line-like marks which are arranged in a rotational direction of the belt member and are formed stepwisely on a surface of the belt member; the marks being tilted from a rotational axis direction of the belt member at least at end portions thereof on sides close to an end surface of the belt member; and control means for controlling rotation of the belt member on the basis of a result of detection of the marks.
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