PURPOSE: To increase rotation interlocking torque of a throttle valve stem by bringing the maximum opening attitude of a throttle valve into an attitude wherein the throttle vale is throttled further to the opening side at a given angle than the axis of the passage of a throttle valve arrangement passage.

CONSTITUTION: The maximum opening attitude 10a of a throttle valve 10 specified based on the minimum extrusion attitude 5a of a governor sleeve 5 is brought into an attitude throttled further to the closing side at a given angle θthan the passage axis 15 of a throttle valve arrangement passage 14 as seen from a direction paralleling the direction of the axis of a throttle valve stem 13. In this way, the opening closing operation range 12 of the throttle valve 10 specified based on the extrusion stroke 11 of the governor sleeve 5 is reduced by a throttle angle 9. Thereby, rotation interlocking torque of the throttle valve stem 13 is increased and the attitude maintaining force of the throttle valve 10 is also increased. In the vicinity of the full opening attitude of the throttle valve 10, even when the throttle valve 10 is throttled to the closing side to some extent, a flow rate of intake air is only reduced slightly and no influence is exercised on a maximum output.