A ball screw device includes a screw shaft, a nut, a ball train including a plurality of main balls, and a plurality of coil springs disposed in the ball train. The nut moves from a first axial side to a second axial side while an axial force is applied to the nut by rotation of the screw shaft. The plurality of coil springs are more densely arranged on the first axial side than on the second axial side in the ball train.