Abstract: An umbrella includes a plurality of ribs for securing an umbrella cloth thereon having at least an intermediate top rib integrally formed with an inner section provided with a downwardly-opened groove in the inner section and an outer section provided with an upwardly-opened groove in the outer section for foldably receiving an inner flexible reinforcing rib into the inner section and for foldably receiving an outer flexible reinforcing rib into the outer section, of which a flexible reinforcing rib is flexibly fastened by a coupling to the intermediate top rib for exerting an elastic force for quickly opening the umbrella for decreasing the chances subjected to attacks by wind or external forces.