PURPOSE: To stabilize a room temp., by means of regulating the drafting quantity to a heater according to the supply or non-supply of the medium to the cooler or to the heater.

CONSTITUTION: A fan 4, a cooler 5, a heater 6, and a damper which controls the drafting quantity to the heater 6 are arranged within a duct 3 which opens to a wheeler room 2, and a thermosensing element 9 is set up in the wheeler room 2. The opening degree of a damper 7 is regulated from an amplifier 15 for temp. control via electricity air convertor 16 and a negative actuator 17, by means of selecting one among three variable resistors 10 in parallel, by changing over a switch 14 by an AND circuit 13 due to the supply or non-supply of a valve 12 of warm water circuit to the heater 6 with an electromagnetic clutch 11 of the compressor in the cooling circuit of said cooler 5 and the signal of the thermosensing element 9. The variable resistor 10 determines the opening control property of the damper 7.