A multichamber air conditioner which is provided with a unit for obtaining the characteristics which are approximately conformable to the reverse characteristics of the desired control dynamic characteristics, an integrator, a unit for receiving the detected room temperature as the input of the above described reverse characteristics unit, comparing the output of the above described reverse characteristic unit with the set value, inputting the compared results to the above decided integrator, controlling the opening of the expansion valve by the output of the integrator, outputting the integration gains of the above described integrator in accordance with the open air temperatures, the total sum of the number of driver stands, the performance, and the variation in the compressor suction pressure.