PURPOSE: To improve the diving environment of a diver in the scuba diving.

CONSTITUTION: With the second stage S, an intermediate pressure pipe 10 for supplying the air which is primarily decompressed in the first stage is connected through a joint 10a. Further, the discharge port 11a of an exhaust pipe 11 connected with an exhaust stay is set long so as to be positioned behind the diver's face. The vicinity of the discharge port of the exhaust pipe 11 is charged with the porous substance 12 such as sponge. When a diver breathes air through a mouthpiece 13, exhaust is discharged into water from the discharge port 11a of the exhaust pipe 11. Since the air bubble formed by the exhaust is formed small by the porous substance 12, the noise due to the air bubbles is weakened, and the diver's viewfield is prevented from being obstructed, and the excellent diving environment can be secured.