Abstract: A positioning device having a high rigidity and smooth positioning characteristics. The positioning device holds a piston formed integrally with a table within a cylinder and has pressure-adjusting elements in two pressurizing chambers in the cylinder partitioned with the piston. A gas is ejected into a clearance between the piston and the cylinder to hydrostatically support the piston. The emitted gas is introduced into the two pressurizing chambers to drive the piston and the table by the pressure difference between the pressurizing chambers. The pressure-adjusting elements include nozzles for emitting the gas in the pressurizing chambers and pressure-adjusting bodies for changing the opening degree of the ejecting port of the nozzles.