PURPOSE: To obtain a mold having little development of casting flash by packing molding sand composition blending the specific quantities of the specific binder and hardening agent into the sand particles for casting into a metallic mold possible to hold to the fixed temp., heating and hardening the molding sand composition.

CONSTITUTION: Into the sand particles for casting, 0.5 - 3 wt.% acid hardening type binder to the sand particles as the binder and 30 - 50 wt.% phosphoric acid water solution at the ratio so as to become 5-15wt.% the phosphoric acid to the binder as the hardening agent are blended. The blended molding sand composition is packed into the metallic mold possible to hold to the fixed temp. in the range of 100 - 200°C and heated to harden the molding sand composition. As the metallic mold temp. is comparatively low, the development of gap be tween mating faces of the metallic mold caused by deformation of the metallic mold is prevented and the mold having little development of casting flash can be obtd.