To provide a method for printing both-side of a sheet to obtain a high degree of glossiness on a front printing side by improving a method for printing both-side of a sheet in a printer used also as a both-side printer.

While each sheet 32a, 32b and 32c is traveled in a printer 31 used also as a both-side printer, each sheet is printed by including: a first step in which each sheet is conveyed to a first body 13 of the printer 31, and at the time, the first body 13 is adjusted in temperature to a first temperature T13 and a first sheet surface 33 is printed; a second step in which each sheet is reversed using a reversing device 5 of the printer 31; and a third step in which each sheet is conveyed to a second body 16 of the printer 31, and at the time, the second body 16 is adjusted in temperature to a second temperature T16 different from the first temperature T13 and a second sheet surface 34 is printed.