To provide an air purifier having a function of collecting duct and a deodorizing function with long service life.

In an air purifier consisting of a dust collecting electrode 4 for generating ozone and also collecting the dust in air, a high voltage generating circuit 4a for applying high voltage to the dust collecting electrode 4, an ozone decomposition catalyst 5, a fan motor 8, a smoke sensor 7 for detecting the contaminated concentration in the air, a microcomputer 9a for controlling the fan motor 8 based on a signal of the smoke sensor 7, and a manually operated switch transmission part 3, a function selection means for determining whether it is operated as a deodorizer or operated as a dust collector from a signal of whether there is an ozone sensor 14 or the ozone decomposition catalyst 5 is provided.