There are provided a sheet conveying apparatus and an image forming apparatus, which enable stable sheet conveyance without depending on sheet size.An air suction portion having a duct portion for air suction is provided inwardly of an endless belt having a plurality of suction holes. Air is taken in through the suction holes of the endless belt and the duct portion for air suction by the air suction portion to absorb a sheet onto the endless belt. When the sheet having a sheet conveying direction length in which a sheet trailing end reaches the endless belt before a sheet leading end reaches a fixing device is conveyed, at least part of the portion of the duct portion through which the sheet trailing end passes before the sheet leading end reaches the fixing portion is closed by a shutter.