Abstract: A gap for allowing the cutting chips to escape is formed between the hole saw side wall and the workpiece in order to enhance the piercing efficiency. This hole saw comprises a drill part for determining the center of piercing with respect to the workpiece, a tubular part possessing plural piercing knives at the end surrounding the circumference of the drill part, and a shank part for fixing the drill part and the rear part of the tubular part and transmitting the torque from a power unit to the both, whereby at least the piercing knife disposition positions of the tubular part possess portions sequentially different in the distance from the rotary shaft.