To provide a method for preventing a body from being torn off by a corner of an end part of a joint of a beam and a head part of a bolt even if a vehicle comes into contact with a guard rail and preventing a torn-off metallic piece from getting in a clearance in the end part of the joint of the beam and the head part of the bolt and to provide a biting prevention device for facilitating its mounting.

In the joint part of the beam having corrugated cross section and used for the guard rail, inclined faces rising gently from a face in a recessed part of the beam toward a face in a top part are provided at both ends on an advance direction side of the vehicle, and a member whose face in the top part protrudes more than a face in a projecting part of the beam in the direction of height after mounting is attached to it.