In an ink supply amount adjusting method for this printing machine, reference opening amounts of ink fountain keys are obtained in accordance with image area ratios of respective areas, corresponding to the ink fountain keys, of a plate by following a preset relationship between an image area ratio and opening amounts of the ink fountain keys. The obtained reference opening amounts are uniformly corrected with preset correction values, thereby obtaining set values of the opening amounts of the ink fountain keys. An ink supply amount adjusting apparatus is also disclosed.