To provide casting sand in a dry state using sodium silicate and sodium metasilicate that has fluidity at ordinary temperature, upon molding, a core having sufficient strength can be molded by the heating of a mold for molding without requiring high temperature steam from the outside and facilitates collapsibility and the regeneration treatment of the casting sand after casting.SOLUTION: A casting sand in a dry state is obtained by coating the surface of silica sand with at least one kind of sodium silicate and sodium metasilicate and hydrous fired kaolin and has fluidity at ordinary temperature, and can mold a core by thermal hardening.