PURPOSE: To automatically control an air conditioner in an ideal state at all times by fixing it to outside air introduction, when the outside air temperature is lower than the inside air temperature in starting the air conditioner in summer season and after inside air circulation and outside air introduction are repeated, fixing it to the inside air circulation.

CONSTITUTION: A damper valve 7 driven by an actuator 8 is provided in a boundary part of outside/inside air introduction ports 2, 3 of a duct 1 and an outer air temperature sensor 16 and an inside air temperature sensor 17 are provided in the upstream side of the outside air introduction port 2 and a place flowing out from a ventilator blow-off port 5 respectively. A controller receives the detection signals of both temperature sensors 16, 17, outputs a control signal, and switches the inside air circulation and the outside air introduction. In starting an air conditioner in summer season, when the outside temperature is lower than the inside air temperature, it is fixed to the outside air introduction and when the inside temperature becomes lower than the outside air temperature, the inside air circulation and the outside air introduction are repeated so that when the inside air temperature becomes sufficiently lower than the outside air temperature, it is fixed to the inside air circulation. Therefore cooling performance can be improved during summer season and the operation rate of the compressor is reduced during winter season, so as to prevent window glasses from being misted.