To enhance removing efficiency of moisture or oil components in compressed air by keeping an adiabatic expansion chamber in which a radiator is housed in the mid-way of a feed path for leading the compressed air of an air compressor to a condensation chamber at almost atmospheric pressure and jetting the compressed air in a drying chamber to the adiabatic expansion chamber from an orifice.

A dryer 22 consists of a cylindrical body 23 and an adiabatic expansion chamber 24. The inside of the body 23 is divided into two chambers by a filter 25 to make the upper side a drying chamber 26 and the lower side a condensation chamber 27. A radiator 30 of a spiral pipe is housed in the adiabatic expansion chamber 24. One end of the radiator 30 is projected to the outside of the adiabatic expansion chamber 24 and connected to the OUT port of an air compressor 20 and the other end therof is passed through the drying chamber 26 and the filter 25 and opened to the condensation chamber 27. An opening on the adiabatic expansion chamber 24 side of a connecting path 34 for connecting the drying chamber 26 and the adiabatic expansion chamber 24 is made to an orifice 36 from which the compressed air from the drying chamber 26 is jetted. By cooling effect in company with the adiabatic expansion of the compressed air jetted to the adiabatic expansion chamber 24 through the orifice 36, the condensation of moisture and oil components in the compressed air is accelerated.