After the end of a preceding print job, a printing press is stopped, and ink form rollers (6-1 to 6-4) of an ink roller group (6) are thrown off. After that, a printing plate (7) is exchanged with a printing plate (7′) of a next print job, and a blanket (91) mounted on a blanket cylinder (9) is cleaned. The opening amounts of ink fountain keys (4-1 to 4-n) corresponding to the image of the printing plate (7′) of the next print job are obtained. The obtained opening amounts of the ink fountain keys (4-1 to 4-n) are corrected by correction values of the opening amounts of the ink fountain keys (4-1 to 4-n) considering the influence of cleaning of the blanket (91) to obtain corrected opening amounts. In a state in which the opening amounts of the ink fountain keys (4-1 to 4-n) have been set to the corrected opening amounts, a corrected ink film thickness distribution corresponding to the image of the printing plate (7′) of the next print job is formed on the ink roller group (6).