Abstract: A gas pressure-reducing valve in which a valve member to be seated on a valve seat opened at its central portion with a valve hole leading to a pressure-reducing chamber between a body and a diaphragm is fixed on a valve stem coaxially extending through the valve hole, and in which the valve stem is fastened to a fastened member fixed on the central portion of the diaphragm. The fastened member is provided with a fitting bore opened at its one end on the side of the valve stem and a bottom threaded bore having a diameter smaller than that of the fitting bore and coaxially leading to the other end of the fitting bore. The valve stem is provided at its end portion on the side of the diaphragm with a fitting stem portion to be fitted in the fitting bore and an externally threaded portion capable of being screwed in the threaded bore and coaxially leading to the fitting stem portion. The externally threaded portion has a shorter axial length than that of the fitting bore.