・Under-reaming bit (SUPER JAWS): This method is DTH hammer drilling system by protecting bored hole by outer casings when drilling the ground formation easy to collapse. After drilling, well casings and screens can be safely and securely installed through the inside of outer casings which are left inside bored hole. ・Reverse circulation hammer (MACH drill): Drilling is carried out by DTH method and removal of cuttings are carried out by reverse circulation system effectively. Especially, this method is suitable for drilling works on the sea or on the river for foundation piling for bridge and jetty, etc.