To prevent the indent and crack of cast products by combining a fixed lead plate and moving lead plate and changing the height of the lead plates in accordance with the sand-metal ratio of molding sand charged to the cast product.

When the sand-metal ratio of the molding sand to the cast product is small and information that the min. molding sand is charged is issued, each small cylinder 10 is contracted and rolling balls 11 are pulled up. As a result, moving circular-arcuate plates 6 are outside pushed up by the repulsion force of coil springs 7, the moving plates 9 are pulled back through connecting rods 8 and their tips are made to coincide with the tip faces of the fixed lead plates 3. Next, when the information that the max. molding sand is charged is issued, each the small cylinder 10 is extended, the moving circular-arcuate plates 6 are pushed out on the side of the rotary drum 4 and the moving lead plates 9 are projected from the tips of the fixed lead plates 3.