To solve the problem that an average injection rate can be measured by a mass flow meter but it is difficult to measure the injection rate per shot and an injection variation in a gas injector.

In a measuring test device measuring a gas injector characteristic, a first chamber 1 and a second chamber 7 are provided at the downstream side of the gas injector 100, incompressible fluids 2 are enclosed in the chambers, respectively, leaving spaces 1a, 7a, and floats 3, 8 are floated. The first chamber 1 is connected to the injector so that gas by the gas injection of the gas injector 100 can be introduced in the space 1a, and the second chamber 7 is connected to the first chamber 1 so that the incompressible fluid 2 can move between the first chamber 1 and the second chamber 7. The gas injection rate per shot, the injection variation or the like can be measured.

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