An outdoor umbrella includes an operation device including a ring-shaped slider joint slidably connected to a shaft of the outdoor umbrella in a vertical movable manner, a locking stopper fitted in a locker hole of the shaft in an inwardly movable manner, a resilient element unit for applying an urging pressure against the locking stopper to normally urge and retain the locking stopper extending into the locker hole so as to lock up the slider joint on the shaft, and a handle means for driving the locking stopper in an outwardly movable manner to move away from the locker hole so as to unlock the slider joint from the shaft.