A prism used for analysis utilizing a surface plasmon is configured by a dielectric medium having a predetermined refractive index. The trapezoidal prism is provided with: an incidence surface on which excitation light from outside is incident; a reflection surface by which the excitation light incident on the incidence surface is reflected; an emission surface from which the excitation light reflected by the reflection surface is emitted; and an opposite surface facing the emission surface and the reflection surface. The opposite surface is a concave-shaped sink mark surface.
