A detection apparatus includes: a first light source group having a plurality of light sources; a switch that switches the plurality of light sources to activate at least one of the light sources, a first optical system that introduces light from the activated light source into an electrical conductor of an optical device; and a detector that detects Raman scattering light from the light scattered or reflected by the electrical conductor. Each of the plurality of light sources of the first light source group is capable of radiating light having different polarization directions.