Abstract: An electrolytic drainage treating apparatus is provided to treat a drainage containing a suspension of contaminated compound whereby the suspension is flocculated and removed by aluminum ions or iron ions eluted by electrolysis. The electrolytic drainage treating apparatus is equipped with a high speed electrolyzer comprising an anode and a cathode having a thin gap therebetween through which a drainage is forcibly passed as an electrolytic solution. The anode material such as aluminum and iron is eluted as ions by the electrolysis caused by passing electric current across the gap. The width of the gap between the anode and the cathode is controlled. The high speed electrolyzer is effectively used for various electrolytic treatments.