Ball screw apparatus

A ball screw apparatus comprising:

• a ball nut including an inner periphery, a ball track formed in the inner periphery, and a first stopper;
• a ball screw shaft including an outer periphery and a ball track formed in the outer periphery, the ball screw shaft being inserted through the ball nut;
• a ball train including a plurality of main balls housed in a raceway formed between the ball track of the ball nut and the ball track of the ball screw shaft;
• a first coil spring including a first end that engages with a first end of the ball train and a second end supported by the first stopper and housed in the raceway;
• and
• a first stopper ball interposed between the first stopper and the second end of the coil spring and having a larger diameter than the main balls, wherein:
• the first stopper includes a first recessed portion formed in the inner periphery of the ball nut, and the first stopper ball is held in the first recessed portion and interposed between the first recessed portion and the second end of the first coil spring;
• and
• the first recessed portion includes a first surface serving as a bearing surface that supports the second end of the first coil spring via the first stopper ball and a second surface that intersects the first surface to define a bottom surface of the first recessed portion, and in a surface of the first stopper ball, an elastic pressing force from the first coil spring is applied to only an intermediate area between a first opposite position that is on the opposite side of the first stopper ball from a first contact point at which the first stopper ball contacts the first surface, and a second opposite position that is on the opposite side of the first stopper ball from a second contact point at which the first stopper ball contacts the second surface.