An air conditioner for a vehicle includes an air conditioner case having an evaporator and a heater core installed therein and having a blower installed at an inlet thereof; a movable filter moving between an air-filtering location and an air-non-filtering location of the air conditioner case; a judging device judging whether air blown by the blower inside the air conditioner case is contaminated; and a driving device moving the movable filter to the air-filtering location when the judging device determines that the air is contaminated and to the air-non-filtering location when the judging device determines that the air is not contaminated. Therefore, when it is determined that the air is contaminated, the movable filter is moved to the air-filtering location. When it is determined that the air is not contaminated, the movable filter is moved to the air-non-filtering location.