Abstract: A locking device for an extendible tube assembly has: an extendible tube, an enforced locking block and a controlling member. The extendible tube includes an inner tube and an outer tube, an end of the outer tube having a through hole on a pivoting base. The enforced locking block has a first end and a second end, the second end includes an indented portion that provides a resting edge; the second end of the enforced locking block is inserted in the through hole of the outer tube such that the resting edge of the second end makes contact with the inner tube in the outer tube. A pivoting portion of the controlling member is provided with an eccentric block, another end of the controlling member is provided with a handle; the pivoting portion of the controlling member is pivoted onto the pivoting base of the extendible tube.