A metal diaphragm valve includes a body with a valve seat provided to a valve chamber communicating a primary flow path and a secondary flow path, a metal diaphragm having a center portion disposed above the valve chamber, the center portion vertically moving to make contact with the valve seat, and a stem provided above the metal diaphragm so as to be able to freely ascend and descend to cause the center portion of the metal diaphragm to move downward. A flow-path restriction part is provided to a part of the secondary flow path. The metal diaphragm valve is quite suitable as a valve for ALD process, the valve favorably reduces fluctuations of a Cv value due to deformation of a resin-made valve seat with time even after the valve is opened and closed at a level of ten million times while a fluid at high temperatures is flowing.