There is provided a particle detector that can increase a detection sensitivity to fluorescence emitted from biogenic particles. A particle detector for detecting biogenic particles includes a substrate having a principal surface and configured to collect the biogenic particles on the principal surface, a light emitting element configured to irradiate particles collected on the principal surface with excitation light, and a light receiving element configured to receive fluorescence emitted from the particles when the particles are irradiated with the excitation light from the light emitting element. An optical axis of the Fresnel lens and a ray direction of the excitation light intersect with each other. The principal surface is a mirror surface.