An image forming apparatus comprising: an image forming portion that forms an image on a sheet of paper; a first route that feeds the sheet of paper to the image forming portion; a second route that feeds again the sheet of paper, on a surface of which the image is formed, to the image forming portion; a sheet adjusting portion that adjusts a deflection of the sheet of paper along a sheet-width direction that is perpendicular to a sheet conveying direction of the sheet of paper fed to the image forming portion; a sheet conveying portion that conveys the sheet of paper, on a surface of which the image is formed, to the sheet adjusting portion by conveying rollers, the sheet conveying portion being provided on the second route at an upstream side of the sheet adjusting portion; characterised by a control portion that is configured to control the sheet adjusting portion and the sheet conveying portion, wherein during a duplex printing mode, the control portion controls the sheet adjusting portion to alternately feed the sheet of paper fed from the first route and the sheet of paper fed from the second route to the image forming portion and the control portion controls the sheet conveying portion to release the contact of the conveying rollers after it is detected that the sheet of paper reaches the sheet adjusting portion; and a sheet detecting portion that detects a rear end of the sheet of paper, the sheet detecting portion being provided at an upstream side of the sheet conveying portion, wherein the control portion is further configured to control the sheet conveying portion to contact the conveying rollers based on sheet-rear-end-detecting information by the sheet detecting portion. an image forming portion that forms an image on a sheet of paper; a first route that feeds the sheet of paper to the image forming portion; a second route that feeds again the sheet of paper, on a surface of which the image is formed, to the image forming portion; a sheet adjusting portion that adjusts a deflection of the sheet of paper along a sheet-width direction that is perpendicular to a sheet conveying direction of the sheet of paper fed to the image forming portion; a sheet conveying portion that conveys the sheet of paper, on a surface of which the image is formed, to the sheet adjusting portion by conveying rollers, the sheet conveying portion being provided on the second route at an upstream side of the sheet adjusting portion; characterised by a control portion that is configured to control the sheet adjusting portion and the sheet conveying portion, wherein during a duplex printing mode, the control portion controls the sheet adjusting portion to alternately feed the sheet of paper fed from the first route and the sheet of paper fed from the second route to the image forming portion and the control portion controls the sheet conveying portion to release the contact of the conveying rollers after it is detected that the sheet of paper reaches the sheet adjusting portion; and a sheet detecting portion that detects a rear end of the sheet of paper, the sheet detecting portion being provided at an upstream side of the sheet conveying portion, wherein the control portion is further configured to control the sheet conveying portion to contact the conveying rollers based on sheet-rear-end-detecting information by the sheet detecting portion.