Abstract: A throttle valve comprising a first outer peripheral portion linearly contacting an inner wall of an intake passage at a predetermined throttle angle and a second outer peripheral portion formed in the vicinity of a throttle shaft in such a manner as to gently continue from the first outer peripheral portion and not contacting the inner wall at the predetermined throttle angle. With this arrangement, as there is defined a space between the second outer peripheral portion and the inner wall in the vicinity of the throttle shaft, the generation of scuffing and biting of the throttle valve against the inner wall may be prevented. Further, as the first outer peripheral portion of the throttle valve linearly contacts the inner wall at the closing position, the leakage of suction air upon full closing of the throttle valve may be suppressed.