Ozone is diffused into a closed water zone used as a raising bed over a wide range thereof in a short period of time and, before the sterilization effect vanishes, is circulated over a wide bottom layer of the water zone to thereby cause the effective spreading of the sterilization effect of the epidemic-causing fungi, virus or the like likely to stay in a part of the water zone interior, water bottom slush surface or coastal water zone. It is thereby intended to strengthen the epidemic-prevention structure based on the sterilization of the entire water zone. A rectifying cylinder 5 interiorly provided with a water jet pump 4 and consisting of a cylindrical body whose both ends are made open so as to improve the water jetting capability of the water jet pump 4 is installed in the water of the closed water zone 1. Ozone is injected into and mixed with the water jetted from the water jet pump 4 and the resulting water is jetted and ozone is thereby diffused into the closed water zone 1 over a wide range in a short period of time. And, ozone is thereby circulated over a wide bottom layer of the water zone before the sterilization effect vanishes.
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