To provide a solidified slag coagulation agent which is economical, can be handled at ease, and prevents occurrence of defects.

The solidified slag coagulation agent 10 is set into a pouring vessel 11 and coagulates floating slag on the surface of molten metal 12 during a casting operation in which the molten metal 12 in the pouring vessel 11 is poured into a mold. The slag coagulation agent in a powder or granular state can be formed into a block having an open hole 13 at the center or at the eccentric position of the block. The slag coagulation agent can be prepared from natural stone containing alkaline component.