1. An image formation system comprising: an image forming section comprising a belt and a roller, wherein the image forming section forms, in a predetermined region of a sheet, either: a first patch image for performing tone correction of a toner image formed on the sheet, or a second patch image for monitoring color variation of the toner image formed on the sheet; and a controller that controls the image forming section to form only one of the first patch image and the second patch image on any one sheet.