PURPOSE: To stabilize combustion at a low rotation area and generate a high output at a high rotation area by controlling a tumble flow according to the running state of an internal combustion engine.

CONSTITUTION: An intake air flow control device for an internal combustion engine comprises a plate 10 which is disposed in the intake air port of an internal combustion engine, is formed in a shape conforming to that of the lower part of the inner surface of the intake air port, is slidable in a longitudinal direction, has a tip 10a in an advancing position protruded in an edge-form manner from the lower end part of an opening end 2a fronting on the combustion chamber 3 of the intake air port 2, is moved away from the opening end in a backward movement position, and controls the tumble flow of air flowing in a combustion chamber, and a drive means to move forward and backward the plate according to the running state of the engine.