In a sterilizing system (100), a sterilizing device (1) receives a supply of oxygen and steam. The sterilizing device (1) produces oxygen plasma containing ozone from the supplied oxygen and discharges the produced oxygen plasma and reactive oxygen produced through reaction between the supplied steam and the oxygen plasma as a sterilizing agent. The sterilizing system (100) also includes an ozone collecting unit (120) for collecting ozone contained in the discharged oxygen plasma.