The present invention provides a conditioning ventilation system 1. In the conditioning ventilation system 1, each of a plurality of rooms in a building is provided with an air-intake portion 16 and an exhaust means 19, the air-intake portions 16 are provided with a plurality of air blowing sections 13 which send wind through a plurality of ducts 17, a return air path which joins up from a plurality of the exhaust means 19 and returns to the air blowing sections 13 is provided, indoor air is circulated in the building by the air blowing sections 13, an outdoor air introduction path having an opening/closing mechanism is connected to the return air path, each of the plurality of rooms is provided with an exhaust means 26 directing to outdoor and having an opening/closing mechanism 27, outdoor air and indoor air are circulated in the building and, in this state, switching operation can be carried out to discharge air to outdoor independently in the plurality of rooms, energy saving and comfortable space having uniform temperature and excellent air quality is normally realized, and when harmful material flows in or is generated, the harmful material is prevented from being dispersed to another room while swiftly discharging the harmful material, and heat and air quality of return air are effectively utilized.