To prevent an impulsive sound generated by a collision of an automatic dropping device and a knocking head when dropping the automatic dropping device along a rod up to the knocking head in a standard intrusion test.

This sound arrester is composed of a lower cover 17 for covering a lower part of the knocking head 11, an upper cover 16 for covering an upper part of the dropping device on the stroke upper end of the dropping device and a peripheral surface cover 20 connected to the upper cover 16 and the lower cover 17 and covering an outer peripheral surface of the freely movable dropping device.