To prevent vibration of a pressure regulating valve in a low flow rate area.
This pressure regulating valve has a control pressure chamber C and a pressure regulating chamber P partitioned by a diaphragm 15, a valve body 17 displacing in the axial direction together with the diaphragm 15, and a valve seat 23 for abutting on and separating from the valve body 17. The pressure regulating valve is constituted so that when diaphragm pressing force by fluid in the pressure regulating chamber P is larger than diaphragm pressing force from the control pressure chamber C side, the diaphragm 15 opens a fluid discharge passage 22 by lifting the valve body 17. A shape of the valve body 17 and the valve seat 23 and a diametrical dimension of the fluid discharge passage 22 are set so that the relationship between a fluid flow rate Q (liter/time) flowing in the fluid discharge passage 22 and a lift quantity X (m), becomes Q X 0.46, within a range being smaller than 150 (m) in the lift quantity X of the valve body 17 to the valve seat 23.
MATSUBARA MAMORU
MURAKAMI KENICHI
HANAI AKIHIRO
