To simplify and lighten a structure of an injector capable of adjusting a mixing ratio of fuel and oxidizing agent.

This rocket engine injector 1 has a truncated cone shaped fuel inlet 5 provided on an upper part of an injecting hole 7, and a propellant regulating bar 4 is provided thereon for free moving in an upward/downward direction. An area of a gap between the fuel inlet 5 and the propellant regulating bar 4 is thereby changed to work as a fuel regulating valve. An oxidizing agent inlet 6 is pierced to a part of a propellant regulating bar 4 positioned in an oxidizing agent chamber 2. The oxidizing agent inlet 6 functions as an oxidizing agent regulating valve since an inlet area thereof is changed with upward/ downward moving of a bulkhead 8 and the propellant regulating bar 4. A structure can be simplified and lightened by reducing the number of valves with providing these two valves inside the injection device 1.