A seat track includes a stopper. The stopper includes a hole formed in a first rail and a stopper main body that projects in a direction of intersecting with a relative sliding direction of a second rail from an edge portion of the hole and is configured to restrict a move of a retainer. When a distance between centers of two steel balls disposed at both ends in the relative sliding direction of the second rail is L1 among steel balls and a distance between inner walls of the hole in the relative sliding direction of the second rail is L2, L1≥L2.