A particle detector includes a light source, and a metal layer having an incident/reflective surface and a photoelectric surface opposing the incident/reflective surface. Incident light from the light source reaches the incident/reflective surface to excite near-field surface plasmon resonance photons at the photoelectric surface. A particle deposited on the photoelectric surface of the metal layer changes the near-field surface plasmon resonance photons to far-field scattered light. The particle detector further includes a scattered light detecting unit, provided above the photoelectric surface of the metal layer, for detecting the far-field scattered light.