Image formation condition is available, which hardly causes imperfections of the image quality. A full-color image formation system selects plural secondary transfer conditions in a secondary transfer unit within a specific range, forms test charts according to each of the secondary transfer conditions selected, and prints them out. A user checks by viewing the test charts printed on each recording sheet, and selects a page number of the sheet where the user evaluated an image quality as the best; and the image formation system sets the secondary transfer condition for the sheet as a standard secondary transfer condition thereafter.