A sample analyzer such as a Rutherford backscattering spectrometer for detecting ions that are elastically scattered by a sample is provided. A spectrum-measuring unit is shifted so that it can be positioned in accordance with a plurality of the scattering directions of the scattered ions in the sample analyzer. For example, the spectrum-measuring unit is shifted in an arc about the irradiation point of the ion beams along a guide rail. Alternatively, a vacuum container is composed of a fixed container holding the sample therein and a movable container hermitically and slidably connected to the fixed container and provided with detection ports. The movable container slides and thus the detection ports are shifted so that the detection ports can be positioned in accordance with the scattering directions. Accordingly, the detection ports, in turn, detection angles are easily changed, whereby a large sample can be analyzed.