PURPOSE: To provide characteristic of constant output from middle speed to high speed by providing a rotary vale in the intake system of the engine, and by controlling a supercharging quantity to be constant regardless of engine rotational speed by means of an air flow quantity passing through an intake passage upstream from a turbo supercharger.

CONSTITUTION: Respective valves 11a-11d for opening/closing branches 9a-9d of an intake manifold 9 leading to respective cylinders 12a-12d are arranged by penetrating the intake manifold 9, in an integral type rotary valve 11, and operated by rotation of a crank shaft 13 via gear rows 14, 15 and a valve opening/closing taming adjusting mechanism 16. An opening/closing timing of a rotary valve 11 is adjusted by transferring an adjusting piece 22 right and left sides via an adjusting lever 23 by means of a pneumatic cylinder 25 in the valve opening/closing timing adjusting mechanism 16, and two chambers 30, 31 divided by a piston 27 are provided in the pneumatic cylinder 25, and connected to the small diameter part 34a, an the large part 34b of a venturi of an air flow rate meter 34 interposed in the air flow-in passage 34 of a supercharger, respectively.