An imaging device (10, 12) comprising: an optical filter on which a plurality of four types of filters (X, Y, Z, T) are arranged in a predetermined manner, the plurality of four types of filters including: three types of filters (X, Y, Z) configured to selectively transmit light of a visible light region having different wavelengths from each other and to have spectral transmittances equal to each other in a near infrared light region, and one fourth type of filter which either transmits only near infrared light or an entire visible light region including near infrared light, an image pickup element including a plurality of pixels which receive light transmitted through the optical filter, convert the received light into an output signal in accordance with luminance of incident light incident to each of the pixels, and output the output signal from each of the pixels, wherein the optical filter is formed on a light-receiving surface of each pixel such that one of the four types of filter is arranged on the light-receiving surface of each pixel; a near infrared light ratio calculating part which calculates a ratio of near infrared light component contained in the output signal for each of the pixels; and an infrared separating part which removes, by a removal rate determined in accordance with the ratio of the near infrared light component, the near infrared light component from each of the output signals for each of the pixels to generate an infrared-separated signal; wherein the infrared separating part is configured to continuously change the removal rate such that the removal rate becomes zero when the ratio of the near infrared light component is from 0% to the beginning of a predetermined range or when the ratio of the near infrared light component is from the end of the predetermined range to 100%. an optical filter on which a plurality of four types of filters (X, Y, Z, T) are arranged in a predetermined manner, the plurality of four types of filters including: three types of filters (X, Y, Z) configured to selectively transmit light of a visible light region having different wavelengths from each other and to have spectral transmittances equal to each other in a near infrared light region, and one fourth type of filter which either transmits only near infrared light or an entire visible light region including near infrared light, an image pickup element including a plurality of pixels which receive light transmitted through the optical filter, convert the received light into an output signal in accordance with luminance of incident light incident to each of the pixels, and output the output signal from each of the pixels, wherein the optical filter is formed on a light-receiving surface of each pixel such that one of the four types of filter is arranged on the light-receiving surface of each pixel; a near infrared light ratio calculating part which calculates a ratio of near infrared light component contained in the output signal for each of the pixels; and an infrared separating part which removes, by a removal rate determined in accordance with the ratio of the near infrared light component, the near infrared light component from each of the output signals for each of the pixels to generate an infrared-separated signal; wherein the infrared separating part is configured to continuously change the removal rate such that the removal rate becomes zero when the ratio of the near infrared light component is from 0% to the beginning of a predetermined range or when the ratio of the near infrared light component is from the end of the predetermined range to 100%.