PURPOSE: To prevent increase of operation cost and waste of energy in an air-conditioning facility.

CONSTITUTION: In an air-conditioning facility, in which air, produced by conditioning induced outdoor air, is sent by a fan 14 to a shop 2 in a building, the number of people who have entered the building is grasped by counting the number of parking cars in a parking area 7 through a gate controller 11 of the parking area while the number of revolution of the fan 14 is changed by a fan control board 13 in accordance with the result of grasping. According to this method, the amount of outdoor air, induced into the shop 2, is changed in accordance with the number of people in the shop 2 whereby the economical operation of the fan is permitted.