To provide a microbial carrier which is high in treatment function, hardly occurs the closing of a filter bed and is easily backwashed and to provide an apparatus for anaerobically treating waste water by using the microbial carrier.

The microbial carrier to be used for the waste water treatment apparatus is composed of a plurality of supporting carriers. Each of supporting carriers has a supporting member and fiber bundles arranged vertically on the supporting member in two or more stages. The fiber bundle consists of a plurality of filaments. One end or the middle of the fiber bundle is fixed to the supporting member in a bundled state and the other end or both ends of the fiber bundle are used as free ends of filaments. The plurality of supporting carriers are arranged side by side so that free ends of filaments of the adjacent supporting carriers are made to overlap one another.