To enable a nonstationary flow rate of a compressible fluid including a reciprocating flow to be generated continuously and precisely.

A continuous nonstationary flow rate generator is equipped with: a flowmeter 12 for measuring an inflow amount of the compressible fluid; a first servo valve 13 for regulating the inflow amount; a first isothermalized pressure container 14 for holding the compressible fluid in an isothermal condition; a first pressure gage 15 for measuring a pressure in the first isothermalized pressure container 14; a second isothermalized pressure container 16 which is held in its vacuum state by a vacuum source; a second pressure gage 17 for measuring a pressure in the second isothermalized pressure container 16; a second servo valve 18 for selectively regulating the outflow from the first isothermalized pressure container 14 or the inflow to the second isothermalized pressure container 16; a third pressure gage 19 for measuring an outward pressure of the second servo valve 18; and a flow rate control means 22 for controlling the outflow amount from the second servo valve 18, based on the inflow amount and the pressure in the first isothermalized pressure container 14, and controlling the inflow amount of the compressible fluid from the second servo valve 18, based on the pressure in the second isothermalized pressure container 16 and the outward pressure of the second servo valve 18.