To secure safety without installing any safety valve in a separate pipe, to realize reduction in space and cost, and to regulate a pressure on the input side of a pressure reducing valve equally in connection to a hose via a single component.

In this pressure reduction adjustment device, compressed air at a primary pressure, which is fed from a compressor and set to a high pressure, inside a pressure tank 5 is decompressed to a secondary pressure lower than the primary pressure by means of a pressure reducing valve 20. A housing 22 for the pressure reducing valve 20 is provided with a primary pressure side passage 23 for the compressed air, a secondary pressure side passage 24 after pressure reduction, a valve element 25 throttling the compressed air from the primary pressure side passage to supply it to the secondary pressure side passage 24. A valve port 39 is opened in the primary pressure side passage of the housing 22, and the valve port 39 is equipped with a safety valve 21 releasing the primary pressure side passage 23 to the atmosphere when the primary pressure becomes a predetermined pressure or more.