Ventilating system including a case mounted on a ceiling of a room, an inlet in a bottom surface of the case, and an outlet in a side surface of the case, a partition for dividing the case into an upper space, and a lower space, a fan in the upper space of the case, for drawing room air through the inlet, and discharging through the outlet, a filter assembly at the outlet for purifying air being discharged to the room, a first duct in communication with the upper space of the case for guiding outdoor air into the case, and a second duct in communication with the lower space of the case for guiding the room air introduced into the case to an outside of the room, thereby providing a ventilating system having an air purifying function.