A mosaic image generating apparatus comprises: a segmenting unit which segments a target image into a plurality of blocks; a target image processing unit which calculates, as a target density value, an average density value of each basic color in each of the blocks; a determining unit which determines from the plurality of blocks a placement block on which the material image is to be placed, without being restricted by the image of the placement block; a calculating unit which calculates an average density value of each basic color in the material image; and a color correcting unit which performs a color correction on the material image such that the average density value of each basic color in the material image becomes the target density value of each basic color in the placement block while maintaining the density value distribution ratio of each basic color in the material image.