This unnecessary matter detection system is provided with: a first lighting system, a second lighting system, an image-capturing system, and a processing system. The first lighting system irradiates food with first light including a first wavelength. The second lighting system irradiates the food with second light including a second wavelength different from the first wavelength. The image-capturing system captures images of the food to which the first light is irradiated and the food to which the second light is irradiated. The processing system determines unnecessary matter to be present in the food, when a region in which a differential absolute value of pixel values between corresponding pixels is a threshold value or greater is present in a first captured image of the food to which the first light is irradiated and a second captured image of the food to which the second light is irradiated.
