PURPOSE: To enhance the characteristic of turning into fine particles and the inter-cylindrical distribution as well as to prevent deviation of the air-to-fuel ratio from its set value during transient operation by furnishing a suction neg. pressure sensor, a number-of-revolutions sensor, a two-fluid fuel injection nozzle, etc.

CONSTITUTION: Upon receiving a signal from a suction neg. pressure sensor 5 and a signal from a number-of-revolutions sensor 6, a control unit 7 emits a signal to drive the valve element 19 of two-fluid injection nozzle 9a. Thereby the valve element 19 is driven to open and close a fuel jet 16. The fuel is sent by a puel pump into a fuel passage 18 via a fuel piping 8 under the control of a fuel pressure regulator, which is to hold the fuel injection pressure constant, and injected out of said fuel jet 16 into an air passage 17. The injected fuel is turned into fine particles by the air 17g, which is introduced through an air piping 12 and flowing in said air passage 17.