A heat exchanger of a ventilating system includes: heat exchange plates having first air passage through which indoor air being discharged to outside of a building passes and a second air passage through which outdoor air being introduced to the interior of the building passes which are sequentially formed: first corrugation plates attached to the first air passage; and second corrugation plates attached to the second air passage, wherein the heat exchange plates are made of a paper material with numerous fine holes that are able to generate a capillary phenomenon and loess which radiates far infrared ray. Heat exchange and moisture exchange between the indoor air and the outdoor air are performed simultaneously, and a cleaning function of removing a harmful material contained in outdoor air can be carried out.