A valve device for an exhaust gas recirculation system of an internal combustion engine, which device has a diaphragm mechanism having a diaphragm to form at least one chamber which is connected to an engine port and has a valve member connected to said diaphragm via a rod to open the valve member against a force caused by a spring acting on the diaphragm, when a vacuum signal of a predetermined level is transmitted from the engine port. The device includes means for allowing adjustment of the position of the diaphragm with respect to the rod and means for securing the diaphragm to the rod after said adjustment of the position of the rod is perfected. Therefore, the EGR valve which is opened at the constant vacuum level can be obtained, with a minimum number of parts requiring high accuracy.