The invention relates to a positioning device. The positioning device comprises a shell, a positioning sleeve arranged in the shell, guide rail rods located on the two sides of the positioning sleeveand used for clamping a workpiece, and a driving device for driving the guide rail rods to move. According to the positioning device, by means of a dual-rail clamping and positioning manner and the structure with the positioning sleeve, the positioning sleeve achieves a guide and auxiliary positioning function, the lower end of the workpiece is inserted into the positioning sleeve, the portion, screwed with other workpieces, of the upper end of the workpiece is exposed, and screwing work can be carried out conveniently.