To provide a inspection system inexpensively available without making any design change of piping and the like to an existing gas piping system used in semiconductor manufacturing processes and the like, and inspecting a mass flow controller in a short period of time, based on an exact reference volume.

A mass flow controller inspecting system is provided with: an inspecting gas line KL disposed in parallel with a branch gas line SL and merging into a post-merger gas line ML; a reference volume calculation section 32 calculating the reference volume prescribed by the piping itself of the gas piping system GS, an inspecting parameter calculation section 33 calculating testing parameters, based on time series data of a measurement pressure to be measured by a pressure measuring means 213 during flow rate control by the mass flow controller 1 to be tested; and a comparison section 33 comparing reference parameters to be set based on the reference volume with the testing parameters.