PURPOSE: To improve excavating workability by generating a rotation force and thrust by means of one and the same device.

CONSTITUTION: When a drive ring 5 is rotated counterclockwise, a driven gear 7 geared with a ring gear 6 is rotated counterclockwise. When the axis of a drive roller 8 is in parallel with the axis of a rod R, the rod R is only rotated clockwise by means of the drive force of the drive roller 8 through rotation in a counterclockwise direction of the driven gear 7. On the contrary, when, through slight rotation in a counterclockwise direction of a lower case 10, the axis of the drive roller 8 is inclined based on the axis of the rod R such that the component of force in a horizontal direction of the drive force of the drive roller 8 is pointed to below, a rotation force is generated at the rod R by means of the component of force in a horizontal direction of a drive force, down thrust is generated by means of a component of force in a vertical direction and excavation is carried out. Reversely, when the drive roller 8 is inclined in a reverse direction through slight rotation of the lower case 10 in a clockwise direction, a rotation force is generated at the rod R by means of the component of force in a horizontal direction of a drive force and up thrust is generated by means of a component of force in a vertical direction to lift the rod.