A control valve comprising: a body having an inlet port through which a fluid is introduced, an outlet port through which the fluid is delivered, a valve hole in a fluid passage connecting the inlet port and the outlet port, and a pressure chamber separated from the fluid passage by a partition; a valve element disposed in the fluid passage and configured to move toward and away from the valve hole to adjust an opening degree of a valve section; a power element including a housing forming the pressure chamber between the body and the housing, and a diaphragm having an outer peripheral portion supported by the housing and partitioning an inside of the housing into a closed space separated from the pressure chamber and an open space being open toward the pressure chamber; a disc disposed in the open space and coaxially in contact with the diaphragm; and a shaft extending through the partition and slidably supported in an axial direction thereof, having a first end connected with the diaphragm via the disc and a second end connected with the valve element, and being configured to transmit a drive force in the axial direction caused by displacement of the diaphragm to the valve element, wherein the diaphragm has a corrugated portion between a flat portion and the outer peripheral portion, the flat portion having a contact surface with which the disc is in contact, the corrugated portion having a concentric circular pattern in plan view and a corrugation pattern in cross-sectional view, the corrugated portion includes substantially N+0.5 corrugations (72, 74), N being a natural number, each corrugation (72, 74) protruding toward a pressure chamber side relative to a reference surface, the reference surface being a surface on the pressure chamber side of the outer peripheral portion, the corrugations (72, 74) being formed between the outer peripheral portion and the flat portion, characterized in that a height of each of the N corrugations of the corrugated portion between the outer peripheral portion and the flat portion is smaller than a height of the flat portion, the heights each being a height toward the pressure chamber side relative to the reference surface in an unloaded condition. a body having an inlet port through which a fluid is introduced, an outlet port through which the fluid is delivered, a valve hole in a fluid passage connecting the inlet port and the outlet port, and a pressure chamber separated from the fluid passage by a partition; a valve element disposed in the fluid passage and configured to move toward and away from the valve hole to adjust an opening degree of a valve section; a power element including a housing forming the pressure chamber between the body and the housing, and a diaphragm having an outer peripheral portion supported by the housing and partitioning an inside of the housing into a closed space separated from the pressure chamber and an open space being open toward the pressure chamber; a disc disposed in the open space and coaxially in contact with the diaphragm; and a shaft extending through the partition and slidably supported in an axial direction thereof, having a first end connected with the diaphragm via the disc and a second end connected with the valve element, and being configured to transmit a drive force in the axial direction caused by displacement of the diaphragm to the valve element, wherein the diaphragm has a corrugated portion between a flat portion and the outer peripheral portion, the flat portion having a contact surface with which the disc is in contact, the corrugated portion having a concentric circular pattern in plan view and a corrugation pattern in cross-sectional view, the corrugated portion includes substantially N+0.5 corrugations (72, 74), N being a natural number, each corrugation (72, 74) protruding toward a pressure chamber side relative to a reference surface, the reference surface being a surface on the pressure chamber side of the outer peripheral portion, the corrugations (72, 74) being formed between the outer peripheral portion and the flat portion, characterized in that a height of each of the N corrugations of the corrugated portion between the outer peripheral portion and the flat portion is smaller than a height of the flat portion, the heights each being a height toward the pressure chamber side relative to the reference surface in an unloaded condition.