In the sand core 10, the tar reducing agent is included in at least the second coating layer 13, which is the outermost layer, of the coating layers 12 and 13. Thus, the tar, which may be generated from the core body 11 and the coating layers 12 and 13 which are positioned thereinside, can be decomposed into low molecular gases (carbon monoxide, carbon dioxide, water, and the like) by heat of the molten metal. As a result, generation of the tar from the sand core 10 to the outside can be prevented. In this case, since the layer which includes the tar reducing agent is the second coating layer 13 which directly contacts the molten metal, the second coating layer 13 can directly receive the heat of the molten metal, and the tar generation prevention effects can be thereby remarkably obtained. Therefore, generation of defects in cast products which may be caused by clogging in the gas drain can be prevented, and structures of the gas drain of the die and the surroundings thereof can be simplified.