PURPOSE: To reduce the amount of an adsorbent for drying by arranging a drier just before an actuator and drying compressed air to be fed by means of the adsorbent as a drying agent whenever the compressed air is fed to the actuator and utilizing all parts of spent air for regeneration of the adsorbent.

CONSTITUTION: In case of applying a pneumatic circuit to i.e. a pipeline system of a brake, a drier 40 is arranged to the upstream side of a relay emergency valve 10 being an actuator. When treating on a brake pedal, the compressed air introduced through an inlet 14 by the actuation of a brake valve bents the circumference of a rubber plate 52 and is subjected to drying treatment by an adsorbent 22 and fed to the valve 10 via an outlet 16. When stopping the tread on the brake pedal, the compressed air of the inlet 14 side is discharged to the outside through the brake valve and the rubber plate 52 is deformed by the pressure difference caused between the inlet 14 side and the adsorbent 22 side and the dried compressed air of the valve 10 side is allowed to back flow through a throttle 36b and takes off water content from the adsorbent 22 and is discharged through a discharge port 18 and the adsorbent 22 is regenerated.