To provide an image forming apparatus for forming good images on both sides of a sheet even when the sheet is a moisture absorbing sheet.

A loop detecting sensor 20 is provided between a transfer device 204 and a fixing device 7 and a loop amount formed in the sheet S due to difference in sheet conveying speed between the transfer device 204 and the fixing device 7 is detected. A speed control means 30 controlling the sheet conveying speed in the fixing device 7 so that the looped amount in the sheet is a reference amount controls so that the sheet conveying speed is made higher than the sheet conveying reference speed when judging that the looped amount in the sheet exceeds the reference value due to a detected result in the loop detecting sensor 20 and the speed is made lower than the reference speed when judging that the speed is less than the reference value. Furthermore, when an image is formed on a second surface, the sheet conveying speed in the fixing device 7 is controlled, based on an average sheet conveying speed of the sheet conveying speed in the fixing device 7 when the image is formed on the first surface.