Correction values (Δθ1-Δθn) according to image area ratios in ranges of a printing plate of a preceding print job corresponding to ink fountain keys (4-1-4-n) are obtained. Opening amounts (θ1b-θnb) of the ink fountain keys (4-1-4-n) corresponding to the image of the printing plate (7′) of a next print job are corrected by correction values (Δθ1-Δθn) to obtain corrected opening amounts (θ1b′-θnb′). In a state in which ink in an ink roller group (6) has been decreased by scraping and removing it by an ink scraper blade (15) and in a state in which the opening amounts of the ink fountain keys (4-1-4-n ) have been set to the corrected opening amounts (θ1b′-θnb′), an ink film thickness distribution corresponding to the image of the printing plate of the next print job is formed on the ink roller group (6).