PURPOSE: To accelerate the proper propagation of bacteria adherent onto a filter and to maintain the pH value of waste water in a fixed range in a filter bed-type waste water treating apparatus, by using shell fossibles as the filter in the filter bed.

CONSTITUTION: Shell fossiles, which are enormously buried in the country and come into the market as a soil conditioner for an agricultural use, are crushed into granules, and treated with a difficulty water-soluble bacteria-decomposing high molecular material, e.g., a difficulty soluble polyvinyl alcohol resin (degree of saponification ≥75%) or vinyl acetate, by dipping, spraying, atomizing or the like method. The treated fossibles are used as a filter in the filter bed of a waste water treating apparatus. Taking into consideration the shape, compression strength and dissolution speed of the filter, the shell fossiles are crushed into particles having a diameter of 0.2W2mm, cement is added to the crushed fossiles at a rate of 7W25wt%, and the mixture is blended with water, formed and hardened into a desired shape easy to use. Phosphate ore powder and/or an alkali or alkaline earth metal humin salt may be added to buffer the pH variation of the waste water and to collect metal ions, if necessary.