Intended is to form a coat having an appearance of no streak. In the range over a substrate (7) where first printing heads (20a) and second printing heads (20b) overlap, there are mixed the shot positions of a first discharge liquid discharged from the first printing heads (20a) and a second discharge liquid discharged from the second printing heads (20b). It is decided by random numbers which ofthe discharged liquids is shot. A coat (30c) to be formed by mixing the first and second discharge liquids is arranged between a coat (30a) formed by the first discharge liquid and a coat (30b) formed by the second discharge liquid, so that the boundaries becomes obscure to make the streak disappear.