PURPOSE: To discharge excavated soil by sucking it into a soil-discharging tube with high efficiency by a method in which a soil sucking tube is set on the lower part of a frame body, suck ports are formed in the wall of the soil sucking tube, and the central part of the soil sucking tube is connected to the soil discharge tube.

CONSTITUTION: A pair of cutter drums 2 are attached through drum supporters 3 to the lower part of a square box-type frame 1, and a soil sucking tube 5 is attached in parallel with the rotary shaft of the drum 2 to the downside of the frame 1 which is positioned above the intermediate portion of the drums 2. Four suck ports 6 are formed in each of the sloped two faces of the tube 5, and a central pipe 8 is formed in the upper central part of the tube 5 of a triangle cross section and connected to the lower end of a soil discharge tube 7 set vertically in the frame 1. Soil excavated by rotation of the drums 2 and scooped up the intermediate portion of the drums 2 is sucked into the tube 5 through the suck ports 6. The soil is then discharged through the tube 7.