DRILLING DEVICE

PURPOSE: To precisely control the action of varying the increased diameter of an expansion head by means of above-ground control mechanisms by using long-size expansion-head-driving rods. CONSTITUTION: An expansion-head-driving rod 1 including first and second long-size rods 11, 12 is prepared, and an expansion head 4 consisting of first and second expansion blades 41, 42 coupled respectively to the first and second rods 11, 12 is coupled to one end of the rod 1. A rod position detector 5, and a vertical-motion driving portion 7 having first and second hydraulic cylinders 71, 72 for driving the first and second rods 11, 12 respectively are connected to the other end of the rod 1. The increased diameter of the expansion head 4 located under the ground is controlled to be varied in three steps, i.e., first, second and third increased diameters by the rod position detector 5, a rotary driving portion 6, the vertical-motion driving portion 7 and a control portion 8, all of which are installed above the ground. The operator executes the control while watching a display panel provided at the fixed portion 52 of the rod position detector 5, thus ensuring that diameter-increasing control for the expansion head 4 is performed with precision.