PURPOSE: To provide a compressed air dryer capable of making a piping system simpler compared with conventional dryers without the need of introducing an air pressure signal to open a regeneration valve through piping from the outside.

CONSTITUTION: A dryer is equipped with an inlet 31 connected with an air compressor, an outlet 33 connected with an air tank, a regenerable adsorbent 14 arranged between the inlet 31 and the outlet 33, and a regeneration valve DV which is installed in a passage connected with the open air on the inlet side of the adsorbent 14 and normally closed. In a compressed air dryer where a regeneration valve A is provided with a valve disc 54 to close the passage and a movable body 50 which is formed being integral with the valve disk and receives energizing force by outlet pressure in the direction of opening the valve on one end side and receives energizing force by a preload spring 56 in the direction of opening the valve on the other end side, a pressure receiving surface receiving the outlet pressure by area smaller than that on one side of the movalbe body 50 is provided on the other side, and at the same time, when the movable body 50 is moved to the specified value in the direction of opening the valve, a valve SV to exhaust the outlet pressure on the other end side is formed.