This joint structure is formed by joining a pair of steel H-beams at flat end surfaces thereof, each of the steel H-beams having a web, flanges, and fillets, and is provided with: weld metal formed between end surfaces of the flanges; and a load bearing steel plate which is arranged between end surfaces of the webs so that the upper surface and the lower surface can be in surface-contact with the entire end surfaces of the webs, and that the side surfaces can be fused integrally with the weld metal.
