An umbrella includes a shaft, a top cap and a runner. Multiple rib units and multiple stretchers are pivotably connected to the top cap and the runner. The rib units each have a first rib, a second rib and a third rib. The first, second and third ribs are pivotably connected in sequence. A canopy is mounted to the rib units. The second ribs each have a first connection portion on one end thereof, and the first connection portion has a seat which is connected to a link unit. The link unit has a joint which is connected to the third rib. The third rib has a positioning member to position the joint. The third rib and the joint are connected with each other to bear wind force applied to the second rib and the third rib, such that the second and third ribs do not deform.