A sheet processing apparatus includes a sheet conveying unit configured to unwind a portion of a rolled sheet and convey the unwound sheet, a ribbon conveying unit configured to convey a ribbon having thereon a coloring layer that is not visible up to a predetermined temperature and becomes visible above the predetermined temperature, a thermal head configured to transfer the coloring layer on the ribbon to a portion of the unwound sheet, and a cutter configured to cut off a portion of the unwound sheet.