A device for forming a molten solidified body by receiving a molten material discharged from a vitrification device or the like on a lower mold, and a method for forming a molten solidified body and, particularly, to a mold supporting device for forming a uniform molten solidified body such that a height deviation on a mold of a dropping molten material is reduced by providing movement to the mold, and a method for forming an uniform molten solidified body. The mold supporting device and the method for forming a uniform molten solidified body to prevent the formation of a high columnar shape at a specific position by the molten effluent not being uniformly contained in the mold due to the high viscosity thereof, thereby forming a uniform solidified body.