To provide a foundry sand leak preventing device of a conveyer belt having skirts, making frequent replacement unnecessary, obstructing the generation of a gap between the skirt and the conveyer belt to prevent the leak of foundry sand, and also preventing the damage of the conveyer belt.

Two belt-shaped flexible rubber skirts 5, 5 extending in the length direction of the belt conveyer 9, coming in contact with the top surface of the conveyer belt 3 by being curved inward at the bottom ends, and a supporting member 4 for supporting the rubber skirts 5, 5 are installed on the upper both sides of the belt conveyer 9.