A shaft portion and a blade portion provided on a side surface of the shaft portion are included, and the blade portion includes cutting blades arranged in a plurality of lines on a side surface of the shaft portion along a peripheral direction, and arranged in a plurality of stages in an extending direction of a shaft center of the shaft portion in each line. Further, the cutting blade has a radial-direction clearance angle, a tip end-side clearance angle, and a base end-side clearance angle.
