The gas-turbine rotor is composed of a plurality of rotor disks which are placed one next to another in the axial direction thereof and fastened by spindle bolts piercing through all the rotor disks in the axial direction. Each of the rotor disks has annular protrusions on both sides and are joined to the adjoining rotor disks by abutting the top faces of the annular protrusions against the annular protrusions of the adjoining rotor disks. Grooves having semicircular cross sections are formed on the top face of each of the annular protrusions. When the rotor is assembled, the grooves of the adjoining rotor disks join and form circular holes. Cylindrical torque pins having flanges at both ends are fitted into the circular holes formed by the grooves. The surfaces of the inner side walls of the annular protrusions are formed as spherical surfaces. The faces of the flanges of the torque pins which contact the inner side walls are formed as spherical shapes matching the curvature of the spherical surfaces of the inner side walls.