A loop of a transferring material is formed at a position between a secondary transfer nip portion and a fixing nip portion such that a loop amount of the loop of the transferring material, which is formed at the position between the secondary transfer nip portion and the fixing nip portion when a mono-color mode is executed, is larger than a loop amount of the loop of the transferring material, which is formed at the position between the secondary transfer nip portion and the fixing nip portion when a full-color mode is executed. In the mono-color mode, image formation is executed such that primary transfer rollers are separated from an intermediate transfer belt. In the full-color mode, image formation is executed by photosensitive drums.