A heat exchanger of a ventilating system, including a plurality of heat exchanging plates which are laminated at a predetermined interval, a first heat exchange member which is laminated among the heat exchanging plates and is formed in a mesh type to increase turbulence of the outdoor air which flows while being attached on a first air path through which outdoor air passes and a second heat exchange member which is laminated among the heat exchanging plates crossed with the first heat exchange member and is formed in a mesh type to increase turbulence of indoor air which flows while being attached on a second air path through which the outdoor air passes can improve heat transfer performance by increasing turbulence of air by positioning a mesh type heat exchange in a air path through which outdoor and indoor air passes.