A connecting structure includes a hollow member or a half hollow member including two side portions opposed apart to each other; a collar; and a bolt. The collar includes two contact surfaces at both ends of the collar. The two contact surfaces are adapted to respectively abut on the two side portions between the two side portions. At least one of the two contact surfaces is formed with a receiving portion for caulking. Moreover, the collar is formed with a bolt-hole passing through the two contact surfaces. The collar is disposed between the two side portions, and is caulked with the hollow member or half hollow member at a caulked portion formed from at least one of the two side portions toward the receiving portion. The bolt is adapted to pass through the two side portions and the bolt-hole to connect the hollow member or half hollow member with another member.