An ink set having a cyan ink, a magenta ink and a yellow ink. A combination of a cyan, magenta and yellow dye respectively contained in the cyan, magenta and yellow ink is selected so as to satisfy the condition that optical density retentions of images formed by a cyan ink for evaluation containing the cyan dye, a magenta ink for evaluation containing the magenta dye and a yellow ink for evaluation containing the yellow dye, as determined before and after an ozone resistance test with an integral ozone concentration of 800 ppm·hr and before and after a xenon light resistance test with an integral irradiance of 43,800 klx·hr, are 70% or more for each of the inks for evaluation and are such that a maximum value of differences of the optical density retentions among the images formed by the respective inks for evaluation is 15 or less.