PURPOSE: To contact hydrazine to a catalyst rapidly and uniformly and to improve the responsive property by increasing the number of feed tubes to multiply the injectors, and dividing a catalyst chamber responding to the number of the injectors.

CONSTITUTION: Plural injectors 13 (four in the figure) are furnished, and the hydrazine passing from a piping 1 through a tube 3, while a propellant valve 2 is opened, and fed to plural feed tubes 12 is sprayed in an atomized condition. Furthermore, by contacting the hydrazine atomized by the injectors 13 to minute catalyst 14 in a catalyst chamber which is divided by minute meshes 15, the hydrazine is dissolved, heated, and reacted to decompose into a mixture gas of ammonia, nitrogen, and hydrogen. And the decomposed gas is exhausted from a nozzle 8 to the outer space to obtain a thrust.