VENTILATION SYSTEM

A ventilation system (100) includes: an air supply unit that supplies air taken in from outside to an inside of a first room; an exhaust unit that exhausts indoor air from the first room to the outside; and a control unit that controls a volume of air to be supplied by the air supply unit and a volume of air to be exhausted by the exhaust unit. The air supply unit and the exhaust unit of the ventilation system (100) are provided in the first room in a building, the indoor air of the first room being polluted. In a case where the control unit controls the volume of air to be supplied by the air supply unit in the first room and the volume of air to be exhausted by the exhaust unit in the first room in a normal ventilation mode in which the volume of air to be supplied by the air supply unit is equal to the volume of air to be exhausted by the exhaust unit, the control unit controls operation of the air supply unit and the exhaust unit in a specific ventilation mode in which the volume of air to be supplied by the air supply unit in the first room and the volume of air to be exhausted by the exhaust unit in the first room are increased as compared with the volumes in the normal ventilation mode and the volume of air to be exhausted by the exhaust unit in the first room is made greater than the volume of air to be supplied by the air supply unit in the first room so as to put the first room under negative pressure.