To provide a spectrum analyzer that can easily mount a sample and stably press and maintain the sample on a measurement reference surface.

When a lever 9 is pushed down to mount a sample, a ratchet 7 and a cam 6 being connected to the ratchet 7 are rotated. When a stiffening plate 4 and a sample presser plate 2 being connected to the stiffening plate 4 are pushed down, the lever stops and at the same time the sample presser plate stops on the spot. In this case, when the sample is mounted on the sample presser plate and the lever 9 is pushed up, a release lever 12 is pushed by the lever 9 and a ratchet nib 11 is disengaged from the ratchet 7. The freed ratchet 7 and cam 6 are inversely rotated by given spring force, the stiffening plate 4 pushes up the sample presser plate 2 with the spring force of a sample presser plate press member 3, and the sample is pressed onto the measurement reference surface for retaining it.