First and second bore blade portions (4a, 4b) are provided on the outer periphery of a rotary shaft (1) at intervals in the circumferential direction with a rotation axis (1a) as the center. A first bore blade portion (4a) has a continuous blade (6) and a second bore blade portion (4b) has a discontinuous blade (8) having protruding blade edges (10) and indented blade edges (11), which are alternately provided. The distance (R10) in the radial direction of the protruding blade edges (10) is set so as to be greater than or equal to the distance (R7) in the radial direction of a continuous blade (6), and the distance (R11) in the radial direction of indented blade edges (11) is set so as to be smaller than the distance (R7) in the radial direction of the continuous blade (6). Accordingly, the cutting resistance of the bore cutter can be reduced (Fig. 2).