PURPOSE: To prevent the generation of intake air noise owing to surge phenomenon during rapid deceleration by performing control such that a supercharging pressure detecting means is provided and an auxiliary intake air throttle valve is fully opened when it is decided based on the detected value of a supercharging pressure that a supercharging pressure is rapidly increased.

CONSTITUTION: In a diesel engine wherein supercharged air fed with a pressure by means of the compressor 1b of an exhaust gas turbine supercharger 1 is introduced to a combustion chamber 2 through an intake air passage 4, the middle of the intake air passage 4 is branched into a main intake air passage 4a and an auxiliary intake air passage 4b running around the main intake air passage 4a. Control of an EGR amount is carried out through regulation of the opening of an auxiliary intake air throttle valve 6 in the auxiliary intake air passage 4b. In a so formed device, a pressure sensor 15 to detect a supercharged pressure generated downstream from the compressor 1b is provided and an output therefrom is inputted to an ECU 21 togetherwith other sensors. When it is decided that the supercharged pressure of the compressor 1b is rapidly increased, the auxiliary intake air throttle valve 6 is fully opened in priority, and control of EGR taking a rapid deceleration period into consideration is executed.