An electrically driven power steering apparatus is structured such that a large impact on a rack shaft (22) occurs upon an impingement of a steering stopper, and, even when an axial force acting on a ball bearing (25) of a presser member (30) becomes zero, a rotation of the presser member (30) is hindered by caulking c at a thin plate member (30b). Therefore, the presser member (30) does not slacken, and a predetermined axial force can be given again to the ball bearing (25) when the impact dissipates. The thus structured power steering apparatus exhibiting, though the cost is low, an excellent shockproof characteristic and capable of preventing the bearing from coming off a ball screw nut, can be provided.