To reduce the damaging of a valve device and to improve an allowable error for manufacturing by engaging a seat with the valve member of the valve device and making the area of the valve member close to the seat relatively flexible.

A diameter reduced area 50 is provided in a part of the outer surface of a valve member 30 formed in a hollow tube and the valve member 30 is arranged in the direction of the diameter reduced area 50 so as to be brought into contact with the flat surface of a second spacer part piece 34. When the valve member 30 is actuated, because of the existence of the diameter reduced area 50, the end area of the relatively flexible control valve member 30 is formed, the distortion of the end area during use is generated easily and such a distortion is caused to be formed as a small deformation by the second spacer part piece 34. Thus, the damaging of the valve device is reduced and an allowable error for manufacturing is improved.