There is provided a linear actuator including an output shaft formed with a helical groove, a retainer having a cylindrical shape to receive the output shaft therein, and provided with a plurality of concave portions in dotted manner at positions of an inner peripheral surface thereof along the helical groove, and a rotor magnet fixed to the retainer. Balls are retained in the plurality of concave portions, respectively, and when the retainer is rotated, the balls are moved along the helical groove of the output shaft in a state where the balls are retained in the concave portions.