The opening and closing operations of a poppet valve are stabilized by preventing a diaphragm and the poppet valve from being inclined so that the pressure adjusting accuracy of a regulator is increased. For that purpose, the diaphragm is fitted with a piston and the poppet valve for opening and closing a valve seat and the piston is guided for moving in the axial direction with a sleeve by slidably inserting the piston into the sleeve.
