A sample working/observing apparatus possesses a sample holding mechanism. The sample holding mechanism possesses a sample holder holding a sample, and a base detachably supporting the sample holder. Between these, there are detachably provided a rotation support part supporting so as to be rotatable, a slide support part supporting so as to be slidable from a rotation center toward an X-direction, and a butting support part supporting so as to be slidable in the X-direction and a Y-direction. In an upper face, there are provided an X-direction positioning pin and a Y-direction positioning pin, which are disposed along the Y-direction and the X-direction from the rotation center, and butt against one side and the other side of the sample.