A positioning mechanism capable of decreasing width and size and a microscope using the positioning mechanism are provided.The positioning mechanism is provided with a supporting shaft possessing a spherical surface part at a prescribed position and guides disposed substantially parallel to the supporting shaft and is characterized, on the assumption that of the three-dimensional directions, the axial direction of the supporting shaft constitutes the z direction, by the fact that the supporting shaft is nipped by the guides at the position of the spherical surface part and enabled to oscillate on the spherical surface part as a fulcrum in the xy directions and as well slide in the z direction.