PURPOSE: To prevent a sense of incongruity at changeover in the above device to automatically change over blow-out mode at target blow-out temperature by correcting to be a prescribed blow-out mode in the hysteresis temperature range of detected environment signals, when the target blow-out temperature is in the range of hysteresis temperature of blow-out mode changeover temperature.

CONSTITUTION: A target blow-out temperature is computed by a target blow-out temperature computing means 100, and a blow-out mode is selected by a blow- out mode selecting means 200. When the target blow-out temperature is within the hysteresis temperature range of blow-out mode changeover temperature, a blow-out mode correcting means 300 selects a prescribed blow-out mode, corresponding to a prescribed condition in the hysteresis temperature range of the open air temperature Ta and the solar radiation quantity Ts output by environment means 26,28. When the mode is different from the selected mode by the mode selecting means 200, it is corrected to control a mode door. By this constitution, the sense of incongruity at changeover can be prevented.