Multistage supercharging system control apparatus

In the case where a supercharging pressure during operation in the single supercharging mode is less than a target value of the pressure of supply gas at the outlet of the low-pressure compressor in the twin supercharging mode, changeover from the single supercharging mode to the twin supercharging mode is prohibited. Meanwhile, in the case where the supercharging pressure is equal to or greater than the target value, the changeover from the single supercharging mode to the twin supercharging mode is permitted.