PROBLEM TO BE SOLVED: To provide a sterilizer for a fluid, having an enhanced efficiency of irradiating a fluid flowing in a passage with UV light.SOLUTION: There is provided a sterilizer 10 for a fluid, comprising a treatment passage 12 through which a fluid to be sterilized flows, an illuminant chamber 14 in which an illuminant 30 is housed to radiate UV light to the fluid present in the treatment passage 12, a window member 32 disposed between the treatment passage 12 and the illuminant chamber 14 to transmit UV light, a pressure control mechanism 40 for controlling the pressure of the illuminant chamber 14 so as to decrease the difference between the pressure of the treatment passage 12 and that of the illuminant chamber 14.SELECTED DRAWING: Figure 1【課題】流路内を流れる流体への紫外光の照射効率を高めた流体殺菌装置を提供する。【解決手段】流体殺菌装置１０は、殺菌対象の流体が流れる処理流路１２と、処理流路１２内の流体に向けて紫外光を照射する光源３０が格納される光源室１４と、処理流路１２と光源室１４の間に設けられ、紫外光を透過する窓部材３２と、処理流路１２の圧力と光源室１４の圧力の差を低減させるよう光源室１４の圧力を調整する圧力調整機構４０と、を備える。【選択図】図１
