An image forming apparatus/method transports a sheet to an image forming unit that can form images on both sheet sides. The sheet is fed to the image forming unit at a predetermined image formation start timing for the first side image formation, thereafter is reversed, and re-fed to the image forming unit for the second side image formation while the first side image-formed sheet waits at least one of sheet waiting positions. A full state, where all the sheet waiting positions are full of the first side image-formed sheets, is detected. The number of sheets transported is controlled so that it is greater than the number of the sheet waiting positions. When the full state is detected, the sheet re-feeding is controlled so that a head sheet among the first side image-formed sheets waiting at the sheet waiting positions is fed in advance of the predetermined image formation start timing.