Abstract: An indirect evaporative cooling apparatus in which a substrate is disposed between a wet channel used to induce an evaporation phenomenon and a dry channel through which cooled air passes, the wet channel and the dry channel are arrayed in layers in an alternating manner, the substrate is cooled by the evaporation phenomenon occurring within the wet channel, substrates that cool the air in the dry channel by heat transfer are layered and disposed, wherein the substrate forming the wet channel and the dry channel is formed by a plastic sheet; a substrate is used in which a plurality of projections are formed as spacers on one side of the substrate of the wet channel and the dry channel, and numerous projections are formed by emboss-patterning on the surface of the substrate on which the spacers are formed and dimples are integrally formed on a back surface.