PURPOSE: To make a large opening area and at the same time to facilitate an adjustment of a degree of opening of dampers by a method wherein a major damper and an auxiliary damper are oppositely arranged to enable their linear movement to be performed to each other, air at the inlet port can be primarily and secondarily adjusted and each of the dampers is adjustably operated with a cam, respectively.

CONSTITUTION: A major part of an air supplying device is composed of a casing 2, inlet port 3, outlet port 4, auxilairy damper 5, main damper 6, auxiliary cam 7 and main cam 8. The auxiliary damper 5 is supported by the casing 2 in such a way as it may be moved linearly, one side of the damper is provided with a valve seat 15 and is formed of such a shape as cylinder to make always a cummunicated passage with the inlet 3. The main damper 6 is supported by the casing 2 in such a way as it may be moved linearly so s to be moved toward or away therefrom and may be abutted against the valve seat 15 of the auxiliary damper 5. Thus, under its open condition, air from the inlet pipe 11 is passed through the interior of the auxiliary damper 5, an opening formed between the auxiliary damper 5 and the main damper 6, a main window hole 20 in a defined box 19, outlet pipe 12 and a blowing port 53 into the interior.