To provide a positioning device having legs composed of parallel links in which external force applied on arms on a link mechanism is converted to force in pulling and compressing directions to improve rigidity for achieving high positioning precision, and a machine tool.

A first arm 20 comprises a first and a second arm members 41, 42 connected to each other by a first connection mechanism 40 provided in the middle to be relatively rotatable around a center axis C1 of the first arm 40, and a second arm 21, 22 comprises a third and a fourth arm members 44, 45 connected to each other by a second connection mechanism 43, 43a provided in the middle to be relatively rotatable around a center axis C2 of the second arm 21, 22. An end part 81 of the first arm 20 and an end part 82 of the second arm 21, 22 are connected to each other by a joint part 46 in such a way that the first arm 20 and the second arms 21, 22 oscillate relatively to each other around an axis D which perpendicularly crosses both the center axis C1 of the first arm 20 and the center axis C2 of the second arms 21, 22.