A post-construction composite anchor bolt is provided having great resistance to a bending moment, even when the reinforcement covering margin is small, and reduces the transformation force caused by the bending moment acting on the joining point between the connecting part and the second anchor bolt, even if the size of the anchor bolt is increased. A post construction anchor bolt in the concrete frame comprising: a first anchor bolt installed projecting outside of a concrete frame; and a second anchor bolt which is eccentrically positioned to the axis of said first anchor bolt and is installed embedded in the concrete frame, and a connecting part which links said first anchor bolt and said second anchor bolt, and is installed embedded in the concrete frame together with said second anchor bolt. Said connecting part is formed to have a portion projecting in the opposite direction to the first anchor bolt, and thus reduces the bending moment which is exerted locally on the connecting part due to the load on said first anchor bolt.