To align a disc in a lower housing which is arranged to abut on a diaphragm by using a power element.

A shaft receiving portion 15c is formed at the center position of the disc 15 and the disc 15 is aligned at the center position of the diaphragm 14 by the shaft 11. Thus, the disc 15 has no contact with an inner peripheral face 12a of the lower housing 12, when separated from the diaphragm 14. The opening end of the shaft receiving portion 15c is wider than the diameter of the shaft 11 and the inner face is tapered to form a gap between the shaft 11 and itself. The inclination of the diaphragm 14 to the axis of the shaft 11, therefore, gives no load that the shaft receiving portion 15c bends the front end of the shaft 11, to the shaft 11. Neither sliding resistance occurs in the lower housing 12, nor increase occurs in the sliding resistance of the shaft 11, to thereby stabilize a set value without causing hysteresis in a valve opening property.