To solve the following problem: a conventional dust collector cools air running through the outside of a swirl flow by cooling the peripheral wall of a dust collecting section and condenses water vapor with dust as a core; however, when minute dust is present at a central portion of the swirl flow, it cannot condense water vapor with the dust as a core, so that it becomes difficult to remove the minute dust.

A throttle opening on the axial line of a dust collecting section is provided and, when air is made to run through the throttle and is introduced into the dust collecting section, the air is subjected to adiabatic expansion to make the dust contained in the air near the axial line condense water vapor.