An image forming apparatus provided with an image forming section forming a reference mark at the position being away from the leading edge of the front surface of a sheet by a prescribed length, and forming an image for the front surface based on the forming position of the reference mark, a transfer sheet reversing section reversing the sheet, a leading edge detection sensor detecting the leading edge of the rear surface of the sheet and a mark detection sensor detecting the forming position of the reference mark on the sheet based on the leading edge of the rear surface of the transfer sheet, and the image forming section forms an image on the rear surface of the transfer sheet based on the forming position of the reference mark on the sheet whose reference point is the leading edge of the rear surface of the transfer sheet.