A testing method for testing a flow controller with high accuracy by shortening as much as possible the time required for the test including the wait time. A testing-subject flow controller and a testing-standard flow controller are arranged in that order in series from the upstream side in a flow channel through which a fluid whose flow is to be controlled flows. In a flow-uncontrolled state in which the valve of the testing-subject flow controller is practically in the full-open state, and with the fluid flow controlled to a predetermined flow rate by the testing-standard flow controller, whether the actual flow-rate measurement according to the testing-subject flow controller falls within a predetermined range of actual flow-rate measurements according to the testing-standard flow controller is determined.