An air conditioner includes an electric dust collector arranged between an evaporator and a heat shield plate. This electric dust collector includes a discharge electrode and a dust collecting electrode. The discharge electrode is applied with a positive polarity of high direct current voltage from a high voltage power source, while the dust collecting electrode is supplied with a negative polarity of high direct current voltage. Accordingly, the dust charged through plus electric discharge by the discharge electrode is attracted onto the dust collecting electrode or a casing thereof.