An air treatment system comprising: an air treatment unit configured to apply predetermined treatment to air passing through the unit; a supply fan unit disposed separately from the air treatment unit and configured to send outdoor air from an outdoor space to the air treatment unit and send the outdoor air treated by the air treatment unit to an indoor space; and an exhaust fan unit disposed separately from the air treatment unit and configured to send indoor air from the indoor space to the air treatment unit and send the indoor air treated by the air treatment unit to the outdoor space; wherein the supply fan unit includes a first fan having a variable rotation speed, and a first airflow volume detection unit configured to detect airflow volume of the first fan or airflow volume corresponding quantity as physical quantity corresponding to the airflow volume, and output a first detection value, and the exhaust fan unit includes a second fan having a variable rotation speed, and a second airflow volume detection unit configured to detect airflow volume of the second fan or airflow volume corresponding quantity as physical quantity corresponding to the airflow volume, and output a second detection value, and wherein the air treatment system further comprises a controller configured to control the supply fan unit and the exhaust fan unit, wherein the controller controls the rotation speed of the first fan in accordance with the first detection value, and controls the rotation speed of the second fan in accordance with the second detection value, characterized in that the controller includes a first control unit provided at the supply fan unit, and a second control unit provided at the exhaust fan unit, the first control unit receives a first command value on the airflow volume of the first fan from outside the supply fan unit, and controls the rotation speed of the first fan in accordance with the first command value and the first detection value, and the second control unit receives a second command value on the airflow volume of the second fan from outside the exhaust fan unit, and controls the rotation speed of the second fan in accordance with the second command value and the second detection value. an air treatment unit configured to apply predetermined treatment to air passing through the unit; a supply fan unit disposed separately from the air treatment unit and configured to send outdoor air from an outdoor space to the air treatment unit and send the outdoor air treated by the air treatment unit to an indoor space; and an exhaust fan unit disposed separately from the air treatment unit and configured to send indoor air from the indoor space to the air treatment unit and send the indoor air treated by the air treatment unit to the outdoor space; wherein the supply fan unit includes a first fan having a variable rotation speed, and a first airflow volume detection unit configured to detect airflow volume of the first fan or airflow volume corresponding quantity as physical quantity corresponding to the airflow volume, and output a first detection value, and the exhaust fan unit includes a second fan having a variable rotation speed, and a second airflow volume detection unit configured to detect airflow volume of the second fan or airflow volume corresponding quantity as physical quantity corresponding to the airflow volume, and output a second detection value, and wherein the air treatment system further comprises a controller configured to control the supply fan unit and the exhaust fan unit, wherein the controller controls the rotation speed of the first fan in accordance with the first detection value, and controls the rotation speed of the second fan in accordance with the second detection value, characterized in that the controller includes a first control unit provided at the supply fan unit, and a second control unit provided at the exhaust fan unit, the first control unit receives a first command value on the airflow volume of the first fan from outside the supply fan unit, and controls the rotation speed of the first fan in accordance with the first command value and the first detection value, and the second control unit receives a second command value on the airflow volume of the second fan from outside the exhaust fan unit, and controls the rotation speed of the second fan in accordance with the second command value and the second detection value.