PURPOSE: To excavate ground subsequently to the breakage of an asphalt subbase course.

CONSTITUTION: In a hydraulic shovel equipped with a working machine 3 in the upper rotary body 2 rotatably provided on the lower traveling body 1, a working machine coupler 11 is fitted at the front end of the arm 8 of a working machine 3 and an asphalt cutter 12 is fitted to the working machine coupler 11 so as to be freely detachable. After an asphalt subbase course has been broken by the asphalt cutter 12, subsequently, the ground can be excavated and hence, a burying work of pipes to be buried can be efficiently carried out.