The control portion controls the sheet adjusting portion to alternately convey the sheet of paper fed from the sheet-feeding path for single-side printing and the sheet of paper fed from the sheet-feeding path for duplex printing to the image forming portion during the duplex printing mode. Images are alternately formed on the front surface of each of the sheets of paper and the back surface of each of the sheets of paper when three sheets of paper are conveyed to the image forming apparatus and they are left therein. 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.
