A method includes: storing a first flow rate from an oxygen mass flow controller for supplying an oxygen with an ozone generator turned off and measuring a flow rate of the oxygen supplied to the ozone generator, and a second flow rate from at least one ozone mass flow controller provided in flow paths; supplying the ozone into a processing container via the flow paths to perform multiple times a predetermined ozone-based process; acquiring a third flow rate from the oxygen mass flow controller and a fourth flow rate from the at least one ozone mass flow controller, by supplying the oxygen with the ozone generator turned off during a predetermined period between the ozone-based processes; and determining whether the fourth flow rate is a normal value by comparing the first and second flow rates with the third and fourth flow rates, respectively.