A hole inner-surface cutting apparatus for cutting an inner surface of a penetrating hole formed in a workpiece, the apparatus comprising: a workpiece hold device that holds the workpiece; a working head capable of being inserted into the penetrating hole, and including a head rotatable body that has a cutting tool for cutting the inner surface of the penetrating hole and is rotatable about a center axis thereof and a head main body that rotatably holds the head rotatable body; a head rotation rod capable of being inserted into the penetrating hole from an end of the penetrating hole, and coupled with the head rotatable body to rotate the head rotatable body by being rotated by a rotation drive source; and a head stroke rod capable of being inserted into the penetrating hole from another end of the penetrating hole, and coupled with the head main body to stroke the working head in an axial direction of the penetrating hole by being stroked by a stroke drive source, wherein a cutting tool shift mechanism (20g, 41a, 41c, 42e) for shifting the cutting tool in a radial direction perpendicular to the axial direction is provided in the head rotatable body of the working head and the head rotation rod, characterized in that: a plurality of positioning mechanisms (22A, 22B, 22C) for positioning the working head along the radial direction in the penetrating hole is provided at at least three positions along the axial direction in the head main body, each of the positioning mechanisms (22A, 22B, 22C) has at least three sliders radially arranged evenly and slidable in the radial direction, guide rollers respectively disposed on distal ends of the sliders and contacting with the inner surface of the penetrating hole, a piston for pressing the sliders outward in the radial direction, and a fluid pressure chamber for actuating the piston, and the hole inner-surface cutting apparatus further comprises a controller configured to control fluid pressures in the fluid pressure chambers of the positioning mechanisms (22A, 22B, 22C) independently from each other. a workpiece hold device that holds the workpiece; a working head capable of being inserted into the penetrating hole, and including a head rotatable body that has a cutting tool for cutting the inner surface of the penetrating hole and is rotatable about a center axis thereof and a head main body that rotatably holds the head rotatable body; a head rotation rod capable of being inserted into the penetrating hole from an end of the penetrating hole, and coupled with the head rotatable body to rotate the head rotatable body by being rotated by a rotation drive source; and a head stroke rod capable of being inserted into the penetrating hole from another end of the penetrating hole, and coupled with the head main body to stroke the working head in an axial direction of the penetrating hole by being stroked by a stroke drive source, wherein a cutting tool shift mechanism (20g, 41a, 41c, 42e) for shifting the cutting tool in a radial direction perpendicular to the axial direction is provided in the head rotatable body of the working head and the head rotation rod, characterized in that: a plurality of positioning mechanisms (22A, 22B, 22C) for positioning the working head along the radial direction in the penetrating hole is provided at at least three positions along the axial direction in the head main body, each of the positioning mechanisms (22A, 22B, 22C) has at least three sliders radially arranged evenly and slidable in the radial direction, guide rollers respectively disposed on distal ends of the sliders and contacting with the inner surface of the penetrating hole, a piston for pressing the sliders outward in the radial direction, and a fluid pressure chamber for actuating the piston, and the hole inner-surface cutting apparatus further comprises a controller configured to control fluid pressures in the fluid pressure chambers of the positioning mechanisms (22A, 22B, 22C) independently from each other. a plurality of positioning mechanisms (22A, 22B, 22C) for positioning the working head along the radial direction in the penetrating hole is provided at at least three positions along the axial direction in the head main body, each of the positioning mechanisms (22A, 22B, 22C) has at least three sliders radially arranged evenly and slidable in the radial direction, guide rollers respectively disposed on distal ends of the sliders and contacting with the inner surface of the penetrating hole, a piston for pressing the sliders outward in the radial direction, and a fluid pressure chamber for actuating the piston, and the hole inner-surface cutting apparatus further comprises a controller configured to control fluid pressures in the fluid pressure chambers of the positioning mechanisms (22A, 22B, 22C) independently from each other.