A valve comprising: a housing part internally formed with an inlet flow path where a liquid flows in, an outlet flow path where the liquid flows out, and a valve hole that leads the liquid from the inlet flow path to the outlet flow path; a valve element part that is configured to come into contact with or separate from a valve seat part disposed around the valve hole to bring the valve hole into a closed state or an open state; and a diaphragm part that is coupled to the valve element part, wherein the diaphragm part includes a base, a tip part that is coupled to the valve element part and inserted into the valve hole, and a bellows part that couples between the base and the tip part and is formed with a peak, a pair of valleys, each valley being adjacent to the peak along the shaft line, and a pair of inclined surfaces inclined from the peak toward the pair of valleys, the peak protruding to the outer peripheral side with the shaft line at the center, a wetted part in contact with the liquid at the tip part is formed in a cylindrical shape extending along the shaft line, the wetted part is inserted into the valve hole and has a fixed outer diameter with the shaft line at the center, in that a lower end part of the bellows part is connected to the wetted part in a connection position coinciding with an outer peripheral surface of the wetted part, and in that the valley of the bellows part is disposed in the same position as the connection position in the radial direction, the valve being characterized in that the valve element part is configured to bring the valve hole into the closed state by bringing a contact part into contact with the valve seat part having a planar shape and orthogonal to the shaft line, to form an annular sealing region, the contact part being formed into an annular shape around the shaft line at the outer peripheral end of the upper end of the valve element part and having a tip part formed in a planar shape. a housing part internally formed with an inlet flow path where a liquid flows in, an outlet flow path where the liquid flows out, and a valve hole that leads the liquid from the inlet flow path to the outlet flow path; a valve element part that is configured to come into contact with or separate from a valve seat part disposed around the valve hole to bring the valve hole into a closed state or an open state; and a diaphragm part that is coupled to the valve element part, wherein the diaphragm part includes a base, a tip part that is coupled to the valve element part and inserted into the valve hole, and a bellows part that couples between the base and the tip part and is formed with a peak, a pair of valleys, each valley being adjacent to the peak along the shaft line, and a pair of inclined surfaces inclined from the peak toward the pair of valleys, the peak protruding to the outer peripheral side with the shaft line at the center, a base, a tip part that is coupled to the valve element part and inserted into the valve hole, and a bellows part that couples between the base and the tip part and is formed with a peak, a pair of valleys, each valley being adjacent to the peak along the shaft line, and a pair of inclined surfaces inclined from the peak toward the pair of valleys, the peak protruding to the outer peripheral side with the shaft line at the center, a wetted part in contact with the liquid at the tip part is formed in a cylindrical shape extending along the shaft line, the wetted part is inserted into the valve hole and has a fixed outer diameter with the shaft line at the center, in that a lower end part of the bellows part is connected to the wetted part in a connection position coinciding with an outer peripheral surface of the wetted part, and in that the valley of the bellows part is disposed in the same position as the connection position in the radial direction, the valve being characterized in that the valve element part is configured to bring the valve hole into the closed state by bringing a contact part into contact with the valve seat part having a planar shape and orthogonal to the shaft line, to form an annular sealing region, the contact part being formed into an annular shape around the shaft line at the outer peripheral end of the upper end of the valve element part and having a tip part formed in a planar shape.