Provided is a diaphragm valve that can resolve the following problem features of disc-shaped diaphragms: a large amount of deformation and easy dust generation; large variations in the capacity of the fluid passage upon opening and closing; and the pressure-receiving area of the diaphragm being large when the passage is closed. A diaphragm (5) comprises: a cylindrical part (21) that is made from a synthetic resin and that fits with a valve stem (4); a bottom wall part (22) that closes the lower end opening of the cylindrical part (21); a flange part (23) that is provided to the upper end part of the cylindrical part (21); and a protruding part (24) that is provided to the central part of the bottom wall part (22) and that faces the upper end opening of the fluid inlet passage (2a). The longitudinal cross-sectional shape of the axially central part (33) of the cylindrical part (21) is formed in a substantially arc shape that protrudes outwards in the radial direction.
