To reduce the pressure loss of fluid and reduce the size of a whole structural body including an inlet pipe 14 by smoothing the flow of secondary air in fluid introduction flow paths 16, 17 extending from an inlet port 15 to a valve port 10 of an ASV 2.

The center axis of the inlet pipe 14 is inclined toward the valve port 10, and an intersecting angle θ to a perpendicular line perpendicular to the center axis of the inlet pipe 14 and to the center axis of a valve stem 12 of a poppet valve 4 is acute, smaller than 90°. Thus, the secondary air flowing from the inlet port 15 into the inlet pipe 14 (the fluid introduction flow path 16) flows almost straight along the center axis of the inlet pipe 14, smoothly curves circularly in the fluid introduction flow path 17, and smoothly flows into the valve port 10 provided in a valve seat 5.