PROBLEM TO BE SOLVED: To provide technique useful to surely reduce possibility of under-water-submersion of a sterilization means for sterilizing water to be treated.;SOLUTION: A treatment tank 127 which performs prescribed treatment of water to be treated, a sterilization means 129 which disinfects the treated water 127a treated in the treatment tank 127 and a water reservoir 131 which stores the treated water 129a disinfected by the sterilization means 129 are installed in a housing to constitute a septic tank. Further the septic tank has a treated water transportation means 155 for supplying the treated water 127a treated in the treatment tank 127 to the sterilization means 129 and a working means 161 which is constituted so that supply of the treated water 127a to the sterilization means 129 by the treated water transportation means 155 is regulated based on water level rise of treated water 131a in a water reservoir 131 in order to prevent under-water-submersion of the sterilization means 129 with the treated water 131a in the water reservoir 131.;COPYRIGHT: (C)2004,JPO
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