Abstract: Shell fossil powder is added to a flocculation agent which is mainly composed of gypsum and silicate compound, and the mixture is added to a suspension. The mixing ratio of the flocculation agent and shell fossil powder is 3:1. The flocculation agent functions as a coagulation core A, and the shell fossil powder is able to absorb grains in the suspension as a carrier B and is acquired by the coagulation core A. The carrier B is a grain which is able to effectively utilize Ca.sup.2+ flocculation site of the coagulation core A, which absorbs a great deal of suspending grains, wherein the suspending grains are acquired by the coagulation core A and form a large flock and are quickly settled.