To improve controllability by minimizing a lag in closing of an exhaust control valve in an exhaust control valve small opening control region entered when a twin-turbo state is switched to a single-turbo state.

When a delay flag F5 is set as the state is switched from twin to single, a count value C3 is incremented by F5=1 (S116). Until a set time elapses, a first exhaust control valve selector solenoid valve SOL. 3 is kept deenergized (S121), thereby closing the exhaust control valve to an opening that allows the small opening control. When C3 becomes T5 or more, a boost pressure control mode evaluation flag F2 is referenced (S120). In the exhaust control valve small opening control region with F2 set to 1, the first exhaust control valve selector solenoid valve SOL. 3 is energized (S122) to enter the mode of the exhaust control valve small opening control. This reduces the lag in closing of the exhaust control valve when control enters the exhaust control valve small opening control region, thereby enhancing boost pressure controllability.