A diaphragm-actuated fluid control valve comprising: - a partition; - a valve for controlling a flow rate or pressure of a fluid; - a valve body with an inlet port, an outlet port, and an orifice provided therebetween, the orifice being adapted to be opened or closed by the valve; and - a diaphragm device adapted to drive the valve in a direction to open or close the orifice, wherein: - the valve, the inlet port, and the outlet port are provided below the partition, - the diaphragm device has a diaphragm and a diaphragm-holding member that fixedly seals the outermost portion of the diaphragm and defines an upper-side pressure chamber between an upper surface of the diaphragm and the diaphragm-holding member as a sealed space, - the valve body defines a lower-side pressure chamber between a lower surface of the diaphragm and the partition such that the lower-side pressure chamber is formed on the partition, - the valve is connected to the innermost portion of the lower surface of the diaphragm via an actuating rod, so that the actuating rod transmits the displacement of the diaphragm to the valve, - a disk member abuts on the innermost portion of the lower surface of the diaphragm, the disk member being urged upward by a compression coil spring that is disposed in a contracted position in the lower-side pressure chamber, wherein - the diaphragm has a mountainous-wave portion formed between the outermost portion and the innermost portion, characterized in that the mountainous-wave portion has the shape of concentric circles when viewed in a plan view and having N + (0.5) elevated portions that protrude upward or downward when viewed in cross section, where N is a positive integer of 3 or less, and - when there is no pressure difference, provided that a bottom surface of the outermost portion of the diaphragm is a reference plane, the difference in elevation between the reference plane and a vertex of each of the elevated portions that protrude downward and the difference in elevation between the reference plane and the inner end (Pe) of the mountainous-wave portion are equal. - a partition; - a valve for controlling a flow rate or pressure of a fluid; - a valve body with an inlet port, an outlet port, and an orifice provided therebetween, the orifice being adapted to be opened or closed by the valve; and - a diaphragm device adapted to drive the valve in a direction to open or close the orifice, wherein: - the valve, the inlet port, and the outlet port are provided below the partition, - the diaphragm device has a diaphragm and a diaphragm-holding member that fixedly seals the outermost portion of the diaphragm and defines an upper-side pressure chamber between an upper surface of the diaphragm and the diaphragm-holding member as a sealed space, - the valve body defines a lower-side pressure chamber between a lower surface of the diaphragm and the partition such that the lower-side pressure chamber is formed on the partition, - the valve is connected to the innermost portion of the lower surface of the diaphragm via an actuating rod, so that the actuating rod transmits the displacement of the diaphragm to the valve, - a disk member abuts on the innermost portion of the lower surface of the diaphragm, the disk member being urged upward by a compression coil spring that is disposed in a contracted position in the lower-side pressure chamber, wherein - a disk member abuts on the innermost portion of the lower surface of the diaphragm, the disk member being urged upward by a compression coil spring that is disposed in a contracted position in the lower-side pressure chamber, wherein - the diaphragm has a mountainous-wave portion formed between the outermost portion and the innermost portion, characterized in that the mountainous-wave portion has the shape of concentric circles when viewed in a plan view and having N + (0.5) elevated portions that protrude upward or downward when viewed in cross section, where N is a positive integer of 3 or less, and - when there is no pressure difference, provided that a bottom surface of the outermost portion of the diaphragm is a reference plane, the difference in elevation between the reference plane and a vertex of each of the elevated portions that protrude downward and the difference in elevation between the reference plane and the inner end (Pe) of the mountainous-wave portion are equal.