To utilize a manifold negative pressure even when a superlean burn engine is employed.

In the manifold negative pressure control device 10 of a superlean burn engine 11, a negative pressure storing chamber 16 is provided to store a negative pressure generated at an intake manifold 12. When a negative pressure force in a negative pressure storing chamber 16 detected by a pressure detecting means 22 is reduced to a value lower than a given value, a throttle valve 15 is regulated by an electronic control unit 23 so that a higher negative pressure is generated in the intake manifold 12.