To enable to accurately measure and test the characteristic of an injector for injecting compressible fluid.

A gas supply flow passage 1 on the upstream side of the injector 100 is provided with a first chamber 11, and a second chamber 21 which is an injection reservoir is provided on the downstream side of the injector 100. A first opening/closing valve 6 is provided on the upstream side of the first chamber 11, and a dynamic pressure first pressure sensor 15 is provided for detecting change in pressure in the first chamber 11 due to injection of gas when the first opening/closing valve 6 is closed. A second opening/closing valve 31 is provided on the outlet side of the second chamber 21, and a relief valve 32 is provided in a flow passage 30 on the downstream side of the second opening/closing valve 31. Characteristic measurement of an injector can be performed without being affected by columnar vibration occurring during gas injection. By providing a mass flow controller 34 in the flow passage 30 on the downstream side of the second opening/closing valve 31, the injection amount can be accurately measured.

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