PURPOSE: To plan how to make compact a device and enhance excavation efficiency by installing a casing tube auger and an auger rod gear to a drive shaft of an earth auger drive motor separately and coaxially and turning both sears relatively.

CONSTITUTION: A casing tube 4 is rotatively driven by way of a bearing 23 with an outer gear by driving a large-sized gear 10 installed to a motor drive shaft 9 of an earth auger rotation drive 6 which is capable of rising freely along a leader of a base machine. An auger rod 5 is rotatively driven by way of gears 19, 20, 18 and 17 and so forth by driving a small-sized gear 11 installed to the drive shaft 9. Two gears 10 and 11 are driven by way of one drive shaft 9 and the casing tube 4 and the auger rod 5 are turned simultaneously and relatively, thereby performing an excavating operation. This construction makes it possible to satisfy a power source with only one system and make compact the device and reduce the weight of the device.