A sheet conveying mechanism, which conveys a sheet on which a toner image has been fixed at a heat-fixing process, includes conveying rollers each of which is a single roller having the same diameter throughout a width for passing the sheet and is disposed in a predetermined section for a cooling process after the heat-fixing process, and includes a sheet conveying guide provided on the predetermined section and having a sheet-passing surface made in the same shape throughout the width for passing the sheet.