PURPOSE: To prevent a throttle adjusting plate from its self-oscillation when a flow control is performed, by providing a diaphragm to be arranged between the throttle adjusting plate, moved deflecting in the direction of a valve seat by an electromagnet, and a cover member.

CONSTITUTION: A cover 6 is equipped with a recessed part 11 which houses a throttle adjusting plate 4, arranged being opposed to a valve seat 2a and an electromagnet 5 and consisting of magnetic material, so as to be able to move deflecting in the axial line direction of a valve seat member 2. A diaphragm 12, consisting of rubber or rubber-state elastic material, is provided to be arranged between the throttle adjusting plate 4 and the bottom surface of the recessed part 11. If an electric current is applied to the electromagnet 5, the throttle adjusting plate 4 moves deflecting to the left by magnetic force generated in accordance with a level of the electric current. Self oscillation of the throttle adjusting plate 4 and its pressing valve unit 5 is absorbed by the diaphragm 12.