A plate-making method for manufacturing a printing plate includes: manufacturing the printing plate based on a knockout method in which knockouts of halftone dots in one color are formed, and halftone dots in the other color are overprinted onto positions of the knockouts; for each of pixels, when a sum of a halftone dot area ratio of the one color and a halftone dot area ratio of the other color is smaller than 100%, forming a gap from a knockout in the one color around a halftone dot in the other color; and for each of pixels, when the sum of the halftone dot area ratio of the one color and the halftone dot area ratio of the other color is greater than 100%, forming an overmask such that the halftone dot in the other color penetrates a periphery of the halftone dot in the one color.