To provide a tool capable of machining different-diameter hole concentricity machined material simultaneously with high concentricity.

A different-diameter hole high-concentricity simultaneous machining tool is composed of a sheath tool 1 comprising in order from the tip to the rear end, a pilot guide part 2, an expanded/contracted small-diameter cutter part 3 with an expanded/contracted slit 3a disposed lengthwise, an expanded/ contracted large-diameter cutter part 4 with an expanded/contracted slit 4a disposed lengthwise, a back guide part 5, and a machine fitting shank 6; an expanding/contracting means 7 pushed into the expanded/contracted small- diameter cutter part 3 from the pilot guide part 2 side; and an expanding/ contracting means 8 pushed into the expanded/contracted large-diameter cutter part 4 from the shank 6 side.