A diaphragm valve includes a valve seat disposed in a valve chamber in a body, an annular groove provided on the outer periphery of the valve seat, a diaphragm provided so as to be able to make contact with and leave the valve seat via a pressurizing device, and a primary-side flow path communicating the valve chamber, in which an inner diameter of a secondary-side flow path contiguously provided to the annular groove is 2.0 to 4.5 times a groove width of the annular groove, and an intersection cross-sectional area between the annular groove and the secondary-side flow path is smaller than a cross-sectional area of the secondary-side flow path and the intersection cross-sectional area is configured to be equal to or larger than 35% with respect to a sectional area of the secondary-side flow path to acquire a predetermined Cv value.