A diaphragm valve which can solve problems of a disc-shaped diaphragm, wherein the amount of deformation is significant and dust is liable to be generated, that the change in volume in opening and closing of the fluid channel is significant, and that a pressure receiving surface area of the diaphragm at the time of channel closure is provided. A diaphragm is formed of a synthetic resin and, a cylindrical portion fixedly fitted on a valve rod, a bottom wall portion closing a lower end opening of the cylindrical portion, a flange portion provided at an upper end portion of the cylindrical portion, and a projecting portion provided at a center portion of the bottom wall portion and facing an upper end opening of a fluid inlet passage. A vertical cross-sectional shape of an axially intermediate portion of the cylindrical portion is formed into a substantially arcuate shape projecting radially outward.