To provide a positioning device of small construction capable of being embodied in a simple constitution and reducing the center height loss.

The positioning device is equipped with a cylinder device consisting of a cylinder, a hollow shaft penetrating the cylinder and furnished with a female threaded portion, a piston fixed to the periphery of the hollow shaft in a position inside the cylinder and a long screw penetrating the hollow shaft of the cylinder device and engaged with the female threaded portion, wherein the cylinder device is moved by rotating the long screw, and the cylinder is moved by supplying and exhausting the hydraulic fluid through a hydraulic fluid inflow and outflow port.