PURPOSE: To reduce the magnitude of sound generated by drop hammer without weakening its impaction by a method in which a noncombustible fibrous substance is provided on the periphery of the drop hammer, and a sand iron layer is provided in the place to be struck by a weight at the lower end of the drop hammer.

CONSTITUTION: The body 10 of a drop hammer H consists of a double cylinder with an outer cylinder 11 and an inner cylinder 12, and a noncombustible fibrous material 13, e.g., glass wool, asbestos, etc., is packed into between the outer and inner cylinders 11 and 12 for enclosing. The sound generated internally is absorbed by the fine fibers of the material 13 and the material is protected from combustion by frictional heat generated in vertically moving a weight 16. An anvil 14 to strike on the head of a pile P is fixed to the lower end of the cylinder 12 and a sand iron layer 15 is formed on the anvil 14. By this, the sound generated when the weight 16 is dropped is absorbed in the particles of the sand iron layer 15.