To clear the restriction on tool volume for waste water by adding a reducing agent to waste water incorporating heavy metal ions, adding a flocculant to separate the liquid and the solids, adding an oxidizing agent to the supernatant, then treating the supernatant with a fluidizing bed type bioreactor.

The waste water incorporating high concentration of heavy metallic ions bonded with ethylenediamine tetra-acetic acid is added the reducing agent to make it to pH of ≥12.0, subsequently is added the flocculant to separate the liquid and the solids, then the supernatant is added the oxidizing agent to lower pH to 7.0, and later the supernatant is fed once to a waste water tank. The water in the waste water tank 1 is fed to an suction port of a circulation pump 6 with a feeding pump 5, and is mixed with the waste water in the circulation tank 3 dissolving oxygen as much as near a saturation state. This waste water is fed to the fluidizing bed type bioreactor 2 and is ejected from the lower part of the fluidizing bed type bioreactor 2, and a value of organic matters in the supernatant is reduced.