Disclosed is an intra-medullary rod, including: a cylindrical body made of an X-ray transmitting material; a plurality of wires, which are made of a material that does not transmit X-ray and are deposited at regular intervals along a surface of the cylindrical body in the circumferential direction, being extended in an axial direction in a spiral shape, wherein each of the wires is made in a way that a starting end and a terminating end of the cylindrical body are connected by the shortest distance along the outer surface thereof. In a fluoroscopic image of the cylindrical body, a distance from a reference position to an intersection location of a pair of the wires corresponds to an amount of rotational angle of the intra-medullary rod. By digitizing the intersection location, the rotational angle of the intra-medullary rod is measured.