An internal permanent magnet motor comprising: a rotor formed by stacking a plurality of steel plates having the same shape, wherein the rotor comprises: an upper stage element stacked by aligning front and back sides of the plurality of steel plates; and a lower stage element formed by aligning front and back sides of the plurality of steel plates wherein the front and back side of the steel plates forming the lower stage element are reversed with respect to the steel plates of the upper stage element, wherein each of the steel plates of the upper stage element and the lower stage element comprises an even number 2n of fastening holes arranged around the center of the steel plates, wherein each fastening hole has a respective reference position, wherein each reference position has the same distance to the center of the steel plate and is positioned where a respective fastening hole would have been positioned if all 2n fastening holes would have been arranged at regular intervals along the circumferential direction, wherein half of the fastening holes (133a, 133c, 133e) is formed at a first interval, wherein the center of each of said fastening holes (133a, 133c, 133e) coincides with its respective reference position, the remaining half of the fastening holes (133b, 133d, 133f) are arranged at a second interval such that the center of each of said fastening holes (133b, 133d, 133f) is positioned away in circumferential direction from its respective reference position by a skew angle (θs) in the same direction, wherein the lower stage element is rotated until all of the plurality of fastening holes of the upper stage element are aligned with all of the plurality of fastening holes of the lower stage element and a skew angle of (θs) is formed between the upper stage element and the lower stage element. a rotor formed by stacking a plurality of steel plates having the same shape, wherein the rotor comprises: an upper stage element stacked by aligning front and back sides of the plurality of steel plates; and a lower stage element formed by aligning front and back sides of the plurality of steel plates wherein the front and back side of the steel plates forming the lower stage element are reversed with respect to the steel plates of the upper stage element, wherein each of the steel plates of the upper stage element and the lower stage element comprises an even number 2n of fastening holes arranged around the center of the steel plates, wherein each fastening hole has a respective reference position, wherein each reference position has the same distance to the center of the steel plate and is positioned where a respective fastening hole would have been positioned if all 2n fastening holes would have been arranged at regular intervals along the circumferential direction, wherein half of the fastening holes (133a, 133c, 133e) is formed at a first interval, wherein the center of each of said fastening holes (133a, 133c, 133e) coincides with its respective reference position, the remaining half of the fastening holes (133b, 133d, 133f) are arranged at a second interval such that the center of each of said fastening holes (133b, 133d, 133f) is positioned away in circumferential direction from its respective reference position by a skew angle (θs) in the same direction, wherein the lower stage element is rotated until all of the plurality of fastening holes of the upper stage element are aligned with all of the plurality of fastening holes of the lower stage element and a skew angle of (θs) is formed between the upper stage element and the lower stage element. an upper stage element stacked by aligning front and back sides of the plurality of steel plates; and a lower stage element formed by aligning front and back sides of the plurality of steel plates wherein the front and back side of the steel plates forming the lower stage element are reversed with respect to the steel plates of the upper stage element, wherein each of the steel plates of the upper stage element and the lower stage element comprises an even number 2n of fastening holes arranged around the center of the steel plates, wherein each fastening hole has a respective reference position, wherein each reference position has the same distance to the center of the steel plate and is positioned where a respective fastening hole would have been positioned if all 2n fastening holes would have been arranged at regular intervals along the circumferential direction, wherein half of the fastening holes (133a, 133c, 133e) is formed at a first interval, wherein the center of each of said fastening holes (133a, 133c, 133e) coincides with its respective reference position, the remaining half of the fastening holes (133b, 133d, 133f) are arranged at a second interval such that the center of each of said fastening holes (133b, 133d, 133f) is positioned away in circumferential direction from its respective reference position by a skew angle (θs) in the same direction, wherein the lower stage element is rotated until all of the plurality of fastening holes of the upper stage element are aligned with all of the plurality of fastening holes of the lower stage element and a skew angle of (θs) is formed between the upper stage element and the lower stage element.