The present invention provides a dust sensor comprising an impactor assembly for passing only relatively small particles among particles contained in air; a light emitting unit for radiating light in a path through which the air introduced through the impact assembly passes; and a light receiving unit for receiving light scattered from particles included in the air passing through the path. The impact assembly may comprise an upper case, a first impactor, and a second impactor. The upper case may include an inlet and an outer downward protruding portion. The first impactor may include a central downward depression and a plurality of slots. The second impactor may include an outlet, a central upward protruding portion, a double-bent portion, an outer upward protruding portion and a guide portion.