PURPOSE: An automatic railing installed in a bridge is provided to prevent damage to a railing part due to the flowing water in flood and reduce secondary damage due to suspended materials contained in the flowing water. CONSTITUTION: An automatic railing comprises a first hinge part(10), a second hinge part(20), a railing part(30), and a railing part hanger. The first hinge part is made of a first bracket and a first hinge. The first bracket is formed in the bridge(B). The first hinge unites with the first bracket. The second hinge part is made of a second bracket and a second hinge. The second bracket is formed on the bridge. The second hinge unites with the second bracket. The railing part is composed of a support(32) and a guardrail(33). The pillar has a first hinge groove to be coupled on the first hinge and to rotate. The guardrail is formed between the pillar and the pillar. The railing part hanger has a second hinge groove to be coupled on the second hinge to rotate. A buoyancy part is formed on the lower part of the second hinge groove. The hanger part is formed in the opposite direction of the bridge around the second hinge groove. The hanger part is composed of a horizontal member and a vertical member. The horizontal member is contacted with the bottom of the pillar of the railing part. The vertical member is contacted with the first side surface of the pillar formed in the railing part.
