A prism used in analysis utilizing surface plasmons is prism of a dielectric medium with a predetermined reflective index. Trapezoidal prism comprises an incident surface on which excitation light is incident from outside, a reflective surface at which the excitation light incident on the incident surface is reflected, an emission surface from which the excitation light reflected by the reflective surface is emitted; and an opposite surface which opposes the reflective surface. The opposite surface is a recessed sink-mark surface.