A dust sensor includes: a main body in which a dust inlet is formed and including an optical sensor and a lens for collecting light scattered by dust which enters into the main body through the dust inlet; a button unit protruding outwardly from the main body and having one end that is inserted into a coupling hole formed in the main body, wherein the button unit is selectively moved, by a pushing operation of a user, upward and downward with respect to an interior of the main body in which the lens is installed; and a cleaner installed on the one end of the button unit that is inserted into the main body, wherein the cleaner is repeatedly brought into contact with the lens by the upward and downward movement of the button unit.