NOVELTY - Organic wastewater containing 1,4-dioxane is subjected to biological treatment, to remove suspended solids and organic substances. The biotic decomposition process is carried out by treating obtained water with microorganism carrier in which the 1,4-dioxane decomposer microbe is supported, to decompose 1,4-dioxane, and the advanced oxidation process decomposition of treated water after decomposing 1,4-dioxane is carried out using ozone, ultraviolet-ray and/or hydrogen peroxide to obtain processed water.    USE - Processing of organic wastewater discharged from manufacturing plants of chemicals and semiconductors, leachate of garbage land reclamation fields and sewage treatment.    ADVANTAGE - The method effectively decomposes and removes 1,4-dioxane in the wastewater, in any type of environment.    DETAILED DESCRIPTION - Organic wastewater containing 1,4-dioxane is subjected to one or more processes chosen from biological treatment, coagulation sedimentation treatment, sand-filtration process, activated carbon treatment and accurate membrane filtration process, to remove suspended solids and organic substances from wastewater. The biotic decomposition process is carried out by treating obtained water with microorganism carrier in which the 1,4-dioxane decomposer microbe is supported, to decompose 1,4-dioxane, and the advanced oxidation process decomposition of treated water after decomposing 1,4-dioxane is carried out using ozone, ultraviolet-ray and/or hydrogen peroxide to obtain processed water. An INDEPENDENT CLAIM is included for processing apparatus of organic wastewater, which consists of combination of two or more apparatuses chosen from biological treatment apparatus, coagulation-sedimentation processing apparatus, activated carbon-adsorption processing apparatus, sand-filtration processing apparatus and microfiltration membrane processing apparatus, arranged in the downstream of suspended solids and organic substance removal apparatus with aeration mechanism inside the tank, biological decomposition treatment device equipped with processing tank in which microorganism carrier is arranged in the downstream of the organism decomposition processor, and advanced oxidation process decomposition treatment equipment arranged in the downstream of biotic decomposition treatment equipment consisting of ozone generator, ultraviolet irradiation device, and hydrogen peroxide supply apparatus.