An image forming apparatus registers both sides of sheets with great precision in a sheet transportation direction in both-side image formation. The image forming apparatus includes: photoconductive drums holding toner images; an intermediate transfer belt temporarily holding the toner images; a secondary transfer roll that transfers the toner images to a sheet in a transfer unit; a registration roll rotating toward the transfer unit being in sheet feeding timing; a fixing unit fixing the toner images transferred to a first side of the sheet; reversion transportation paths reversing the sheet and again transporting the sheet to the transfer unit; a first sensor detecting the image of the first side of the sheet; and a second sensor that detects the toner images held in the intermediate transfer belt.