PURPOSE: To appropriately presume a change of temperature immediately after passing an evaporator so as to control an air mix door in the case where mode is changed from the air conditioner ON mode, which allows the drive of a compressor, to the air conditioner OFF mode, which inhibits the drive of the compressor.

CONSTITUTION: An evaporator temperature supposing means 1 gives a first temperature value at the time of air conditioner ON mode, and gives a second temperature value at the time of air conditioner OFF mode as the temperature immediately after passing the evaporator. In the case where mode is changed from the air conditioner ON mode to the air conditioner OFF mode, an evaporator temperature computing means 2 performs the fuzzy inference of the time constant of the temperature change immediately after passing the evaporator on the basis of the deviation between the first temperature value and the second temperature value and the fan voltage, and computes the temperature immediately after passing the evaporator on the basis this time constant. An air mix door control means 3 controls an air mix door on the basis of the computed temperature immediately after passing the evaporator.