Abstract: A telescoping multi-sectional mast in which the upper sections are extended and retracted in a controlled predetermined sequence an in which each section, when fully extended, is automatically and positively locked to the next lower section. The improved locking system includes a lock bar near the lower end of each lower section, a locking assembly on the upper end of each intermediate section and a lock actuator stud on the upper ends of each of the intermediate and bottom sections. The lock assembly includes an inwardly projecting collar, and rotatable disk having a locking projection segment formed on its periphery, a toggle responsive to vertical movement of the lock bar and stop actuated by the toggle for controlling rotation of the lock disk. The lock actuator stud and lock disk have mating engageable cam surfaces to cause and control rotation of the disk in response to vertical movement of each upper section relative to the next lower section.