EXCAVATION TOOL

An excavation tool, in which a device is provided which receives the striking force of a hammer and the rotational force of a hammer cylinder, in a bottom surface of which at least three axle holes are provided displaced from a center of the device and at equivalent angular intervals in the circumferential direction, block axles are inserted in the axle holes in a freely rotatable manner, blocks which are roughly fan-shaped and have bits embedded in the lead end surfaces thereof are provided at lead end parts of the block axles, so that left- and right-side faces of said blocks are in mutual opposition and arc parts of all blocks together form roughly a circle shape; and when said device is rotated in the direction of excavation, said blocks rotate as a result of the resistance to excavation of the bottom part of the excavation hole, one intersection part of the side faces and the arc part of each block protrudes beyond the outer circumferential surface of the device by a predetermined excavation amount, and the mutual positions of the block axles with respect to the blocks are so determined that both side faces of each block come into contact with the side faces of neighboring blocks at this time.