A particulate concentration detector comprising: a detection mechanism including a light emission unit, which emits light from a light emission surface toward a liquid, and a light reception unit, which receives the light from the light emission unit through the liquid with a light reception surface and detects the amount of light transmitted through the liquid, with the particulate concentration detector detecting the concentration of particulates suspended in the liquid from the amount of light detected by the detection mechanism, the detection mechanism including: a first light transmission unit arranged at a location facing toward the light emission surface of the light emission unit; a second light transmission unit arranged at a location facing toward the light reception surface of the light reception unit; a liquid chamber formed between the first light transmission unit and the second light transmission unit and allowing the liquid to flow therein and flow thereout; characterized in that a third light transmission unit (50, 80) is arranged in an oscillatable manner in the liquid chamber so as to face toward the first light transmission unit and the second light transmission unit, wherein the third light transmission unit (50, 80) is oscillated by movement of the liquid in the liquid chamber or vibration of the detection mechanism, and the third light transmission unit (50, 80) is configured to scrape off stains from the first light transmission unit and the second light transmission unit using the oscillating movement. a detection mechanism including a light emission unit, which emits light from a light emission surface toward a liquid, and a light reception unit, which receives the light from the light emission unit through the liquid with a light reception surface and detects the amount of light transmitted through the liquid, with the particulate concentration detector detecting the concentration of particulates suspended in the liquid from the amount of light detected by the detection mechanism, the detection mechanism including: a first light transmission unit arranged at a location facing toward the light emission surface of the light emission unit; a second light transmission unit arranged at a location facing toward the light reception surface of the light reception unit; a liquid chamber formed between the first light transmission unit and the second light transmission unit and allowing the liquid to flow therein and flow thereout; characterized in that a third light transmission unit (50, 80) is arranged in an oscillatable manner in the liquid chamber so as to face toward the first light transmission unit and the second light transmission unit, wherein the third light transmission unit (50, 80) is oscillated by movement of the liquid in the liquid chamber or vibration of the detection mechanism, and the third light transmission unit (50, 80) is configured to scrape off stains from the first light transmission unit and the second light transmission unit using the oscillating movement. a first light transmission unit arranged at a location facing toward the light emission surface of the light emission unit; a second light transmission unit arranged at a location facing toward the light reception surface of the light reception unit; a liquid chamber formed between the first light transmission unit and the second light transmission unit and allowing the liquid to flow therein and flow thereout; characterized in that a third light transmission unit (50, 80) is arranged in an oscillatable manner in the liquid chamber so as to face toward the first light transmission unit and the second light transmission unit, wherein the third light transmission unit (50, 80) is oscillated by movement of the liquid in the liquid chamber or vibration of the detection mechanism, and the third light transmission unit (50, 80) is configured to scrape off stains from the first light transmission unit and the second light transmission unit using the oscillating movement.