PURPOSE: To simplify an inner mechanism of a damper opening/closing device by a method wherein a changing-over of a set temperature of a third chamber is carried out by adjusting an amount of cold air flowing to a thermo-sensitive cylinder of the damper opening/closing device.

CONSTITUTION: At the midway part of a cold air discharging passage 12 reaching a third chamber 4 is formed a through hole 17 communicating with a storing section for storing a thermo-sensitive cylinder 10a of a temperature adjusting device 9. The side of the through hole 17 at the thermo-sensitive cylinder 10a is opened/closed by a flap 19 of a shutter 18 fixed to a surface of a cover 9c of the temperature adjusting device 9. A damper opening/closing device 20 for the third chamber 4 is operated such that when it is set to its partial state, the flap 19 closes the through hole 17 and a degree of opening of the damper is adjusted under a state in which cold air does not flow in the thermo-sensitive cylinder 10. In turn, when it is set to a chilled state, the flap 19 opens the through hole 17 and adjusts a degree of opening of the damper under a state in which the cold air flows at the thermo-sensitive cylinder 10a. With such an arrangement as above, it is possible to simplify and inner mechanism of the damper opening/closing device.