Abstract: A pile driver is disclosed, in which an adapter for transmitting the hammering force of a hammer provided in a hydraulically driven vibrator to a member to be driven into the ground is provided between the hammer and driven member. The adapter is formed with an oil accommodation section, in which a head portion to be hammered by the hammer is formed. The oil accommodation section is filled with oil such that the head portion is immersed in oil. A cooling unit is provided such that it surrounds the adapter. A cooling medium is circulated through the cooling unit by a circulating unit.