A hollow steering shaft having a good quality can be manufactured at a low cost by passing a blank tube having a circular cross section through a preliminary shaping die and then through a finishing shaping die. The blank tube which has passed through the preliminary shaping die is formed with two kinds of convex curve surface portions having different radii of curvature and arranged continuously, circumferentially and alternately. When the blank tube passes through the finishing shaping die, the larger convex curve surface portions are deformed into flat portions. As a result, a steering shaft having an elliptical cross section is manufactured.