The present invention relates to ventilating systems, and more particularly, to a ventilating system having a heat exchanger for exchanging heat of room air being discharged to an outside of a room with heat of outdoor air supplied to the room. The present invention provides a ventilating system including a case having a first flow passage for guiding outdoor air to a room, and a second flow passage for guiding room air to an outside of the room, and a fan unit in the case, the fan unit having a first side for drawing the outdoor air from the first flow passage, a second side for drawing the room air, and a circumferential side for discharging the outdoor air drawn through the first side to the room, and discharging the room air drawn through the second side to an outside of the room.