An imaging device having an imaging lens and an imaging unit, the imaging device comprising: a visible light measurement unit configured to measure an amount of visible light components; an infrared illumination unit configured to perform infrared illumination; and a control unit configured to cause an intensity of the infrared illumination by the infrared illumination unit to gradually decrease as the amount of visible light components measured by the visible light measurement unit decreases from a first threshold to a second threshold, wherein the visible light measurement unit is configured to measure the amount of visible light components based on information acquired from the imaging unit, characterized by further comprising an infrared cut filter configured to be inserted on or removed from an imaging optical path of the imaging lens, a calculation unit configured to calculate a chrominance component from an image acquired from the imaging unit, wherein if the amount of visible light components is less than or equal to the first threshold, the infrared cut filter is removed from the imaging optical path, the calculation unit is configured to calculate a first chrominance component from the image with the infrared cut filter inserted on the imaging optical path, and is configured to calculate a second chrominance component from the image with the infrared cut filter removed from the imaging optical path, the imaging device is configured to generate a color image with the infrared cut filter inserted on the imaging optical path, and the imaging device is configured to generate the color image or a black-and-white image, according to the first chrominance component, the second chrominance component, and an intensity of the infrared illumination radiated by the infrared illumination unit with the infrared cut filter removed from the imaging optical path, and if the first chrominance component or the second chrominance component is less than a fourth threshold, the imaging device is configured to raise an intensity of the infrared illumination unit to an output upper limit, wherein the fourth threshold is a chrominance value corresponding to the second threshold, at which a color information is not identifiable from an image. a visible light measurement unit configured to measure an amount of visible light components; an infrared illumination unit configured to perform infrared illumination; and a control unit configured to cause an intensity of the infrared illumination by the infrared illumination unit to gradually decrease as the amount of visible light components measured by the visible light measurement unit decreases from a first threshold to a second threshold, wherein the visible light measurement unit is configured to measure the amount of visible light components based on information acquired from the imaging unit, characterized by further comprising an infrared cut filter configured to be inserted on or removed from an imaging optical path of the imaging lens, a calculation unit configured to calculate a chrominance component from an image acquired from the imaging unit, wherein if the amount of visible light components is less than or equal to the first threshold, the infrared cut filter is removed from the imaging optical path, the calculation unit is configured to calculate a first chrominance component from the image with the infrared cut filter inserted on the imaging optical path, and is configured to calculate a second chrominance component from the image with the infrared cut filter removed from the imaging optical path, the imaging device is configured to generate a color image with the infrared cut filter inserted on the imaging optical path, and the imaging device is configured to generate the color image or a black-and-white image, according to the first chrominance component, the second chrominance component, and an intensity of the infrared illumination radiated by the infrared illumination unit with the infrared cut filter removed from the imaging optical path, and if the first chrominance component or the second chrominance component is less than a fourth threshold, the imaging device is configured to raise an intensity of the infrared illumination unit to an output upper limit, wherein the fourth threshold is a chrominance value corresponding to the second threshold, at which a color information is not identifiable from an image.