An automatic leg tube locking device including a hollow cylinder shaped guide switch and a circular truncated cone shaped guide post which are mutually matched for use. Through holes are evenly formed in the side surface of the guide switch, the through holes are adapted with locking shafts, a transmission mechanism is arranged between the guide switch and the guide post, so that the guide switch vertically moves along the inclined cylinder surface of the guide post and drives the locking shafts to move along the guide post when the guide switch and the guide post rotate relative to each other. A photography tripod, a unipod and a crutch are further provided. The automatic leg tube locking device, the photography tripod, the unipod and the crutch are capable of pulling the leg tube to any position and lock the leg tube automatically in a locking state.
