A rotor core of a rotating electric machine, wherein: - the rotor core is configured by laminating annular core pieces in an axial direction while shifting permanent magnetic poles of the annular core pieces in a circumferential direction, the annular core pieces each formed by arranging arc-shaped core pieces side by side in the circumferential direction, - the rotor core comprises: a main welding portion where the arc-shaped core pieces laminated in the axial direction are welded to each other on an inner peripheral surface of the rotor core; and additional welding portions (17; 17-L, 17-U) where arc-shaped core pieces (10; 10-L1, 10-U1) of a first layer and arc-shaped core pieces (10; 10-L2, 10-U2) of at least a second layer are welded to each other in an axial end part of the rotor core only, on said inner peripheral surface of the rotor, - one additional welding portion (17; 17-L, 17-U) from said additional welding portions (17; 17-L, 17-U) is provided with respect to the main welding portion in one side of the axial end part, - another additional welding portion (17; 17-U, 17-L) from said additional welding portions (17; 17-L, 17-U) is provided with respect to the main welding portion in another side of the axial end part, - the additional welding portion (17; 17-L, 17-U) at one end and the additional welding portion (17; 17-U, 17-L) at the other end are provided on different sides of the main welding portion in the circumferential direction, and - the other sides of the main welding portion in the circumferential direction, where said one and said another one additional welding portions (17; 17-U, 17-L) are not provided, are free of additional welding portions. - the rotor core is configured by laminating annular core pieces in an axial direction while shifting permanent magnetic poles of the annular core pieces in a circumferential direction, the annular core pieces each formed by arranging arc-shaped core pieces side by side in the circumferential direction, is configured by laminating annular core pieces in an axial direction while shifting permanent magnetic poles of the annular core pieces in a circumferential direction, the annular core pieces each formed by arranging arc-shaped core pieces side by side in the circumferential direction, - the rotor core comprises: a main welding portion where the arc-shaped core pieces laminated in the axial direction are welded to each other on an inner peripheral surface of the rotor core; and additional welding portions (17; 17-L, 17-U) where arc-shaped core pieces (10; 10-L1, 10-U1) of a first layer and arc-shaped core pieces (10; 10-L2, 10-U2) of at least a second layer are welded to each other in an axial end part of the rotor core only, on said inner peripheral surface of the rotor, a main welding portion where the arc-shaped core pieces laminated in the axial direction are welded to each other on an inner peripheral surface of the rotor core; and additional welding portions (17; 17-L, 17-U) where arc-shaped core pieces (10; 10-L1, 10-U1) of a first layer and arc-shaped core pieces (10; 10-L2, 10-U2) of at least a second layer are welded to each other in an axial end part of the rotor core only, on said inner peripheral surface of the rotor, - one additional welding portion (17; 17-L, 17-U) from said additional welding portions (17; 17-L, 17-U) is provided with respect to the main welding portion in one side of the axial end part, - another additional welding portion (17; 17-U, 17-L) from said additional welding portions (17; 17-L, 17-U) is provided with respect to the main welding portion in another side of the axial end part, - the additional welding portion (17; 17-L, 17-U) at one end and the additional welding portion (17; 17-U, 17-L) at the other end are provided on different sides of the main welding portion in the circumferential direction, and - the other sides of the main welding portion in the circumferential direction, where said one and said another one additional welding portions (17; 17-U, 17-L) are not provided, are free of additional welding portions.