An interior of an air conditioning case is partitioned into a first air passage extending from an inside air suction port to a foot opening portion and a second air passage extending from an outside air suction port is disposed at a side of the first air passage to detect a temperature of air blown out from the evaporator disposed in the first air passage and the second air passage. An operation of the compressor for supplying the refrigerant to the evaporator is intermitted by comparing the temperature detected by the temperature sensor and the set temperature set in advance, and the set temperature is changed to be higher according to an increase in the temperature of outside air. In this way, it is possible to prevent the frosting of the evaporator in winter season, when the inside air is introduced into the first air passage and the outside air is introduced into the second air passage.