PROBLEM TO BE SOLVED: To monitor the operation of a light emitting element while continuously sterilizing a fluid. A fluid sterilizer 10 continuously supplies a flow path 12, a light emitting element 30 for irradiating ultraviolet light toward the flow path 12, and a drive current having a predetermined value to the light emitting element 30. A power source for intermittently supplying a driving current of a plurality of steps different from a predetermined value to the light source 30, a control unit that acquires the driving voltage value and the driving current value of the light emitting element 30, and monitors the current-voltage characteristics of the light emitting element； Equipped with. The power supply may alternately repeat a first period of continuously supplying a driving current of at least one value in a plurality of stages and a second period of continuously supplying a driving current of a predetermined value. [Selection diagram] Figure 1【課題】流体に対して連続的に殺菌処理をしながら発光素子の動作をモニタする。【解決手段】流体殺菌装置１０は、流路１２と、流路１２内に向けて紫外光を照射する発光素子３０と、発光素子３０に所定値の駆動電流を連続的に供給し、発光素子３０に所定値と異なる複数段階の値の駆動電流を間欠的に供給する電源と、発光素子３０の駆動電圧値および駆動電流値を取得し、発光素子の電流電圧特性をモニタする制御部と、を備える。電源は、複数段階の少なくとも一つの値の駆動電流を継続供給する第１期間と、所定値の駆動電流を継続供給する第２期間とを交互に繰り返してもよい。【選択図】図１
