A spectral device includes a polarizing filter and an optical filter. The polarizing filter transmits part of light incident on the polarizing filter, the part of light having a particular polarization component. Light that is incident on and passes through the polarizing filter is converted into linearly polarized light. Light that has passed through the polarizing filter is incident on the optical filter. The optical filter transmits light within a particular frequency range. The optical filter includes a metal layer and a dielectric layer. The dielectric layer is disposed on the metal layer. Multiple slits are formed in the metal layer. The multiple slits are arranged at equal intervals in a predetermined direction. The multiple slits extend in a direction perpendicular to a direction in which the light that has passed through the polarizing filter is polarized.