Abstract: A metal diaphragm valve includes a valve casing, a diaphragm made of an elastic material and having an upward bulge in the center and a valve system in which the diaphragm is operated to close or establish a fluid-flow relationship between an inlet passage and an outlet passage both mounted in the casing. The valve system is separated by the diaphragm from the casing and comprises a vertically shiftably disposed push rod adapted to directly move the diaphragm, a plurality of steel balls arranged in a circular groove of a V-shaped cross section defined in the top surface of the push rod, a vertically movably disposed drive rod having a tapered lower end portion situated above the center of the groove and place in constant contact with the steel balls, and a drive means adapted to move the drive rod. The groove has an outer concentric slope and an inner concentric slope, and the steel balls are normally made to stay in the inner slope of the groove.