In one printing scan of a plurality of printing scans of a multi-scan system, in which an ink dominant on the surface of a printing medium is set, the printing percentage of the ink relatively low in the degree of glossiness is set to be higher than that of the ink relatively high in the degree of glossiness. Thereby, the ink relatively low in the degree of glossiness becomes dominant in an overall image, so that the degree of glossiness is stabilized at a low level, even if the bi-directional printing operation is carried out, or the printing duty varies. Thus, the glossy-banding hardly occurs.