The range hood unit includes a range hood transmitting unit configured to transmit information on an exhaust volume. The heat exchanging ventilation device (1) includes: a heat exchanger receiving unit (19) configured to receive the information from the range hood transmitting unit; and a heat exchanger control unit (17) configured to determine the operation of the heat exchanging ventilation device (1), based on the information received by the heat exchanger receiving unit (19). Based on the exhaust volume of the range hood unit that has been received by the heat exchanger receiving unit (19), the ventilation system exhausts air by subtracting the exhaust volume of the range hood unit from an exhaust volume equivalent to the air supply volume of the heat exchanging ventilation device (1).