Excavation tool

The invention relates to 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, and in a bottom surface of which at least three axle holes (2a; 2b; 2c) are provided displaced from a center of the device (2) and at equivalent angular intervals in the circumferential direction. Block axles (3a; 3b; 3c) are inserted in the axle holes (2a; 2b; 2c) in a freely rotatable manner, and blocks (11a; 11b; 11c) 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 (3a; 3b; 3c) so that left- and right-side faces (12a; 12b) of said blocks (11a; 11b; 11c) are in mutual opposition and arc parts (12c) of all blocks (11a; 11b; 11c) together form roughly a circle shape. When said device is rotated in the direction of excavation, said blocks (11a;; 11b; 11c) rotate as a result of the resistance to excavation of the bottom part of the excavation hole, one intersection part of the side faces (12a; 12b) and the arc part (12c) of each block (11a; 11b; 11c) protrudes beyond the outer circumferential surface of the device by a predetermined excavation amount, and the mutual positions of the block axles (3a; 3b; 3c) with respect to the blocks (11a; 11b; 11c) are so determined that both side faces (12a; 12b) of each block (11a; 11b; 11c) come into contact with the side faces (12a; 12b) of neighboring blocks (11a; 11b; 11c) at this time.