PURPOSE: To reduce installation area and to promote mechanical efficiency.

CONSTITUTION: A power source 5 and a rotary drive 12 are provided to the inside of a sub-structure 2 under a drum 6 provided on the sub-structure 2 and a cat shaft 24. A rotary 11 rotating a drill string 9 is provided under a working floor 18 on the sub-structure 2, the rotary is communicated with the rotary drive 12 by a gearing mechanism 57 provided to the inside of the sub- structure 2. The power source 5 and rotary drive 12, rotary drive 12 and drum 6 and drum 6 and cat shaft 24 are communicated with gearing mechanisms 53, 55 and 60 respectively. The drum 6, cat shaft 24, power source 5 and rotary drive 12 are arranged in three dimensions, so that installation area can be reduced. A power transferring system is simple, so that mechanical efficiency can be promoted. The gearing mechanism 57 is concealed under the working floor 18, so that work efficiency is promoted without obstruction.