Abstract: 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

Abstract: An excavation tool, having a pair of insertion holes placed in the bottom surface of a device, which receives the impact force of a hammer and the rotational force of a hammer cylinder, at positions separated in a radial direction from the center of the device and symmetrical around this center as a center of rotation, also having block axles, one end of each of which is freely rotatably inserted into one of the insertion holes, and having blocks, which have a roughly semicircular shape with a diameter roughly equal to that of the device, into the lead end surfaces of which are set bits, and which have straight edge surfaces which are flat surfaces vertical with respect to the lead end surfaces, provided at the other end of the block axles and with the straight edge surfaces in mutual opposition; in an extended diameter state of the blocks, the blocks are moved in opposite directions along a radius of the device by rotating the blocks around the block axles, and the distance between the centers of the inserti