An image forming apparatus adjusts a size of the loop of the sheet between the fixing unit and the transfer unit, according to a signal from a loop detection unit provided in a sheet conveyance path between a transfer unit and a fixing unit and configured to detect a loop of a sheet. The loop detection unit includes a detecting lever that is provided protrudably and retractably from and into the sheet conveyance path and abuts against the sheet, and a loop detection sensor that is turned on or off by the detecting lever. If the sheet is to be conveyed only by the transfer unit, the detecting lever moves to a retracting position from the sheet conveyance path.