To provide a waste water treatment method and equipment which are capable of sufficiently and efficiently reducing the excess sludge generated in biological treatment of organic waste water and improving cost effectiveness.

The waste water treatment equipment is constituted by connecting to a solid-liquid separation tank 2 to a biological treating vessel 1 to which raw water W is supplied and successively connecting an ozone treating vessel 3 and a solid-liquid separation tank 4 thereto. The water Wk to be treated which is subjected to anaerobic treatment in the biological treating vessel 1 is subjected to separation of a solid from the liquid in the solid-liquid separation tank 2 and part of sludge S is transferred to the ozone treating vessel 3. Ozone-containing gas Go is supplied from a gas supply source 5 to the ozone treating vessel 3 and part of the sludge S is oxidation decomposed. The outflow water containing the sludge S is sent to the solid-liquid separation tank 4 where a separated liquid containing a soluble component and the remaining sludge are separated. While the separated liquid is sent to the biological treating vessel 1, the separated sludge S is returned to the ozone treating vessel 3 and is subjected to cyclical treatment.