A linear actuator displaces a relative position between a guide rail and a slide table, which is arranged in confronting relation to the guide rail. Projections are formed on opposite end sides of the guide rail, the projections extending along a direction of displacement and projecting toward the slide table. The slide table is disposed between the projections on the opposite end sides of the guide rail, with rigid balls being interposed therebetween. Guide grooves and guide grooves, which rollably support the balls, are provided on the projections on the opposite end sides of the guide rail and on the slide table. The guide grooves and the guide grooves apply, on the balls, a pressure caused by a magnetic attractive force of permanent magnets.