An air cleaner for cleaning air and for providing sterilization and deodorization effects, includes an air-liquid contact part, for bringing the air into contact with a water screen formed by spraying, using nozzles, pressurized circulating water, and for removing foreign materials from the air; a liquid separating part for separating from the air, tiny water droplets that are included in the air passing through the air-liquid contact part; a cylindrical body into which air to be cleaned is guided, and in which the air-liquid contact part and the liquid separating part are arranged in order; a chlorine dioxide addition unit, for adding a stabilized chlorine dioxide solution to a water tank for the water that is circulated; and a chlorine dioxide activation unit, for activating chlorine dioxide added to the circulating water, that is arranged in a circulating water pipe that extends from the water tank to the spray nozzles.