To provide a pressure regulator for decompressing a pressurized fluid through a pressure control mechanism, which is miniaturizable and usable for a long time even to a fluid such as a highly soluble gas.

This pressure regulator comprises a housing 2 including an inlet port 21 for supplying a pressurized fluid with a primary pressure from a fluid supply source and a discharge port 22 for discharging the pressurized fluid with a reduced secondary pressure, and a passage extending from the inlet port 21 to the discharge port 22, which is formed in the inner part; and a pressure control mechanism disposed in the middle of the passage to reduce the primary pressure to the secondary pressure. The pressure control mechanism comprises a mobile body 7 including a diaphragm 8 which displaces according to pressure fluctuation of the fluid. The inlet port 21 and the mobile body 7 are arranged in a direction substantially orthogonal to the displacing direction of the diaphragm.