PURPOSE: To improve fuel consumption and drivability, by controlling the titled device so that the given temperature of an evaporator is made to vary step by step through the temperature of air at the inlet of the evaporator and the temperature of either the evaporator or air to be blown off from the evaporator is risen and fallen in the opposite directions of a rising and falling directions of the forgoing temperature varying step by step.

CONSTITUTION: When a cooling load is heavy and the temperature of inflow air into an evaporator is high, divided voltage VA becomes high, levels of comparators OP1 and OP2 become "L", transistors Tr1 and Tr2 are turned ON and divided voltage Vc becomes a high level. On the one hand, divided voltage VB becomes low, a comparator P3 becomes "H" level, a transistor Tr4 is turned ON and a compressor 12 is driven. An instruction temperature, therefore, becomes lowest, as a temperature of the evaporator is lowered rapidly and the divided voltage Vc is on a high side. When the temperature of the evaporator becomes lowest, the divided voltage VB becomes high, the level of the comparator OP3 becomes "L" when the voltage VB becomes more than the voltage VC, a compressor 12 is suspended and the temperature of the evaporator becomes high. With this repeating control, control of air conditioning can be done effectively.