A power transmission mechanism of a shaft and a hub, wherein a shaft tooth part (22) having a plurality of linear spline teeth (20) is formed at the end part of the shaft (12) and a hub tooth part (28) having a plurality of linear spline teeth (26) fitted to the end part of the shaft (12) is formed in the inner peripheral surface of a shaft hole (16) in the hub (14). A first step part (30) is formed by swelling the shaft tooth part (22) toward the hub tooth part (28) from a point (P1) horizontally moved from the center point (P0) of the shaft tooth part (22) to a shaft shank (24) side. On the ridge part (28a) side of the hub tooth part (28), a point (P2) is set at a position offset from the point (P1) horizontally to the opposite side of the shaft shank (24), and a second step part (32) increased in diameter from the point (P2) in the radial outer direction is formed. |