To greatly improve the surface roughness of the inner peripheral surface of a hole, by forming a blade part so that the cutting directions of a rough blade part and a large-diameter finishing blade part is in opposite directions.

A reamer 1 rotating counterclockwise is inserted into the hole of a work piece to cut on the inner peripheral surface of the hole by a rough blade part 3, and is advanced. Then in a condition where the intermediate part 6 of the reamer 1 is advanced to a position opposite to the inner peripheral surface of the hole, the rotation of the reamer 1 is stopped once, and concurrently the rotation is reversed, that is, rotated clockwise to advance the reamer 1 continuously; and the inner peripheral surface of the hole of the work piece is cut by a large-diameter finishing blade part 7. Though a fine protruded flaw is caused along in a rotation direction by cutting by the rough blade part 3 in the inner peripheral surface of the hole, the inner peripheral surface of the hole can be formed into a desired condition by cutting in an opposite direction to the tilt of the protruded flaw by the finishing blade part 7 rotating in the reverse direction thereafter.