PURPOSE: To improve accelerating performance, by ceasing a supercharge pressure restriction control, which restricts the maximum supercharge pressure normally to a preset value or less, while controlling a suspension period of this control in accordance with a deviation of the supercharge pressure in that time from the preset value, when an engine is in accelerative operation.

CONSTITUTION: An engine, providing in its exhaust passage 16 a bypass passage 26 bypassing a turbine 20 of a turbosupercharger 18, interposes in said passage 26 a waste gate valve 28 driven by a diaphragm mechanism 30. The engine actuates the diaphragm mechanism 30 by a supercharge pressure in the downstream of a throttle valve 24 while controls this supercharge pressure by a solenoid valve 44 of normally closed type. A control unit 50 controls the solenoid valve 44 so as to restrict a supercharge pressure in the downstream of a compressor 22 to a preset value or less. While when acceleration is detected by an acceleration detector 48, the control unit controls the supercharge pressure so as to stop this restriction control while here sets a period, for the restriction control to be suspended, in accordance with a difference between the supercharge pressure and the preset value.