PURPOSE: To enable to omit a filter, by providing a separator at an outlet port of cool air for separating a cool air passage and a dust containing air passage from each other, and thereby separating the intake air into clean air and dust containing air without using any special means.

CONSTITUTION: When dust containing air is carried to a cool-air outlet port 14, air is guided helically by a cool-air guide passage 19, so that dust and foreign matter having a large mass are urged raially outwards by the function of the centrifugal force. The dust and foreign matter are collected in a dust guiding passage 20, and while being guided also helically, is separated by a separator 21. Then, the dust-containing air in the dust guiding passage 20 is discharged to the outside from a dust-containing air outlet port 23. Therefore, it is enabled to omit a filter.