To provide a pressure adjuster capable of supplying a stable gas pressure by preventing the fluctuation of a primary pressure from having any influence on a secondary pressure, and canceling the influence of the secondary pressure in a pressure adjuster for adjusting and supplying a high pressure gas from the primary side to the secondary side.

A sealed air chamber with a guide part for guiding the vertical movement of a main valve is formed in a primary pressure flow passage at the lower part of the main valve so as to be separated from the primary pressure flow passage by a barrier plate, and a secondary pressure is allowed to act from a secondary pressure flow passage through the passage in the main valve to the air chamber so that a pressurizing force can be applied from the downward direction to upward (open valve) direction of the main valve. Then, the hole diameter of the guide part of a main valve axial part is formed so as to be made equal to the hole diameter of a valve mouth corresponding to the main valve.