To provide an inexpensive post for a guardrail, and the guardrail for vehicles.

The guardrail post 20 for supporting a horizontal member 10 disposed along a driveway R comprises a base plate 21 fixed to a foundation K constructed along the driveway R; a post body 22 joined to the upper face of the base plate 21 by welding; and reinforcing members 23 joined to the base plate 21 and the post body 22 by welding. The reinforcing members 23 are disposed between a front side reference line which is a straight line abutting on the driveway R side edge of the post body 22 and parallel with the horizontal member 10, and a middle reference line which is a straight line passing through the sectional drawing center of the post body 22 and parallel with the horizontal member 10.