A sheet separating apparatus for a fusing unit separates a sheet being conveyed through a fusing unit from a heating roller and guides the sheet to a discharging roller without causing damages to a surface of a fusing roller. The sheet separating apparatus comprises a separating claw rotatably disposed toward a discharging side of a heating roller, for separating a sheet from the heating roller, and a contact spring pivoting the separating claw so that a front end of the separating claw is in contact with the heating roller with a predetermined constant pressure. The front end of the separating claw has rounded corners. It is preferred that the front end of the separating claw is chamfered. Also, it is preferred that the separating claw is made of stainless steel.