A sheet of paper is set on a paper-supplying portion of a top surface gloss processing apparatus while its top surface is faced upward. A gloss level sensor measures gloss level of the top surface of the sheet of paper. Data of this measurement is compared with a previously set threshold value. Based on this comparison, it is determined whether or not the gloss processing has been performed on the top surface thereof. When determining that the gloss processing has been already performed, a warning message such that the gloss processing has been already performed on the top surface of the sheet, of paper is displayed on a screen. On the other hand, when determining that the gloss processing has not performed, the top surface gloss processing apparatus performs the gloss processing on the top surface thereof.