To provide an air cleaning system capable of preventing the prolonged discomfort of a person present in a room by realizing the optimization of air conditioning efficiency.

This air cleaning system has an air cleaner body 17 having a sucking blower 13 for sucking foul air in the room 11, a dust collecting/deodorizing means 15 for cleaning the foul air 12 and removing dust to make the air purified air 14, and a first fouling degree detection means 16 for detecting the fouling degree of the air, the detection means being provided on the front stage side of the air flow of the dust collecting/deodorizing means 15; an external ventilation device 20 for replacing the inside air 12 with the outside air 19; and a control means 21 for controlling the sucking blower and the ventilation device according to the detection result of fouling degree. This system further has a second fouling degree detection means 22 for detecting the fouling degree of the purified air on the rear stage side of the dust collecting/deodorizing means 15 and controls the rotation speed of the sucking blower13 and the working frequency of the external ventilation device 20 based on fouling degree dtected by the first and secod fouling degree detection means 16, 22.