An image forming apparatus includes an image forming portion forming a toner image on a sheet, a rotatable heating member and a rotatable pressing member for fixing, at a nip, the toner image formed on the sheet by the image forming portion, an executing portion for executing a cleaning mode for cleaning the rotatable heating member by introducing, into the nip, the sheet on which a predetermined toner image is formed by the image forming portion, a re-introducing mechanism for re-introducing the sheet, into the nip, which has passed through the nip and then has been turned upside down, and a shifting mechanism for shifting a sheet position so that when a single sheet is introduced twice into the nip in the cleaning mode by using the re-introducing mechanism, positional relationships of a first-time sheet and a second-time sheet relative to the rotatable heating member with respect to a widthwise direction of the rotatable heating member are made different from each other.