A heat exchanger of a ventilating system includes: heat exchange plates laminated with regular intervals so that a 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 into the interior of the building passes are sequentially formed; first corrugation plates attached to the first air passage and obtaining a space to allow outdoor air to pass therethrough; and second corrugation plates attached to the second air passage and obtaining a space to allow outdoor air to passtherethrough, wherein the heat exchange plates are made of a paper material with numerous fine holes that are able to generate a capillary phenomenon. A sensible heat exchange and a latent heat exchange are possible to minimize a change in a temperature and moisture.