To provide an anaerobic treatment method and an equipment for an organic matter-containing waste liquid which are capable of decreasing the solid contents eluting into a separating liquid and enhancing the sludge concentration of an anaerobic treating vessel by improving the solid-liquid separability of an anaerobic treating liquid and are capable of drastically reducing the volume of the sludge by increasing the amount of the sludge to be subjected to reforming treatment without degrading the efficiency of the anaerobic treatment.

The organic matter-containing waste liquid 5 is introduced into the anaerobic treating vessel 1 and is mixed with return sludge 6 and the anaerobic biological sludge in the vessel, by which the waste liquid is subjected to the anaerobic treatment. The anaerobic treating liquid 9 is introduced into a reforming treating vessel 2 and is subjected to ozone treatment by using an ozone treating liquid 14, by which the sludge is reformed to be easily biodegradable and is improved in the solid-liquid separability. The ozone treating liquid 14 is then subjected to a solid-liquid separation in a solid-liquid separation separator 3. The separated liquid 16 is discharged as the treated water to the outside of the system. The solid contents are returned as the return sludge 6 to the anaerobic treating vessel 1.