PURPOSE: To improve the responsive quality of a supercharging pressure control when the variable control of the supercharging volume of a supercharger is made on the basis of a basic supercharging pressure control quantity in opposition to an engine operation condition, by conducting the open loop control of a supercharging pressure in the case of a valve mechanism valve operation condition being a condition is opposition to a low speed operation sphere.

CONSTITUTION: A turbo charger 7 whose compressor portion 8 and turbine portion 12 are respectively provided at an air intake manifold 3 and an exhaust manifold 11, is constituted so that a supercharging volume may be variable by changing an exhaust gas flow passage cross sectional area to the turbine portion 12 by means of an actuator 18 on the basis of a basic supercharging pressure control quantity in opposition to an engine operation condition. Also, a valve mechanism 14 is constituted so that a valve timing may be variable by controlling through a solenoid valve 16 and a changeover control valve 17 pressure oil. In this instance, the basic supercharging pressure control quantity is corrected according to a difference between the target value and the actual value of the supercharging pressure, and when the valve operation condition of the valve mechanism 14 is in a condition in opposition to a low speed operation sphere, the supercharging pressure is arranged so as to be conducted with an open loop control.