A stand adjustment device has a tripod-connecting member, a connecting seat, two clamping plates, a boom-connecting tube, a locking shaft, and a manual operating member. The connecting seat is rotatably located around the tripod-connecting member. The two clamping plates are detachably attached to two opposite sides of the connecting seat respectively. One end of the locking shaft is movably disposed in the boom-connecting tube. The boom is slidably mounted through the boom-connecting tube and the locking shaft. The locking shaft is slidably mounted through the boom-connecting tube, the two clamping plates, and the connecting seat such that the boom-connecting tube is rotatable relative to the connecting seat. The manual operating member and the locking shaft are configured to clamp the boom-connecting tube, the two clamping plates, and the connecting seat therebetween into a locked condition.