To perform an engine test with a simple device by forming a gas exhausting means into an annular type ejector system to blow out a primary flow from an outer boundary, and feeding it with a part of oil supply to a testing engine as this primary flow, in this engine testing device with the gas exhausting means.

At the time of the combustion test of a rocket engine 30, at an ejector primary flow feeder 32, a part of fuel out of a liquid or gas fuel feeder 31 is received, and it is sprayed from a nozzle hole (a) of an annular type ejector 35 as a primary flow by way of an inlet manifold 33, a cooling passage 28 and an outlet manifold 34 as the specified pressure liquid or gas. With this constitution, the inner part of a chamber 11 is reduced to the specified low pressure, while a supersonic diffuser 12 is cooled as specified. Thus, since fuel being small in molecular weight is utilized as a primary flow of the ejector 35, an outlet velocity in the nozzle hole (a) is accelerated, holding down a mass flow rate to smallness, insofar as possible, and further the primary flow feeder 32 is made to be simple in structure and inexpensive in cost, and besides, special cooling equipment falls into disuse.