PURPOSE: To create a swirl in a suction port and thereby to promote fuel atomization by arranging an auxiliary suction passage bypassing each suction passage of a multi-cylinder internal-combustion engine and tangentially injecting air from the auxiliary passage in the cross-sectional circumferential direction.

CONSTITUTION: A suction passage 15 is communicated with an engine 7, and an auxiliary suction passage 22 is provided which bypasses the passage 15 and communicates the upstream side of a throttle valve 16 with a suction port 4. In the passage 22 is provided an auxiliary throttle valve 23, of which the tip end is formed with a tangential opening 18 directed in the cross-sectional circumferential direction in the port 4. There is provided a fuel injection valve 14 directed to the opening 18. In a low-speed operation of the engine 7, the valve 16 is closed and the valve 23 opened, to inject air in the form of a swirl into the port 4 through the passage 22.