1. An imaging apparatus comprising: a solid-state image sensor having, in a two dimensional array, infrared light-receiving pixels having selective sensitivity to infrared light and configured to output an infrared pixel signal, and a plurality of types of color light-receiving pixels having sensitivity to the infrared light and to visible light of mutually different specific colors and configured to output a plurality of types of color pixel signals each of which corresponds to each type of the color light-receiving pixels; and an image signal processing circuit configured to generate a processed image signal for displaying an infrared composite image in which an enhanced infrared image is synthesized with and displayed on a visible image on the basis of a raw image signal composed of an infrared pixel signal that corresponds to the infrared light-receiving pixels and a plurality of types of color pixel signals that corresponds to each of the color light-receiving pixels, wherein the image signal processing circuit includes: a component image signal generator configured to generate an infrared component image signal that corresponds to an infrared light component, and to generate a plurality of types of color component image signals that corresponds to visible-light components of the specific colors on the basis of the infrared pixel signal and the color pixel signals; an infrared composite synthesizer configured to synthesize, for each of the specific colors, the color component image signal and a signal obtained by multiplying the infrared component image signal by a gain of the specific color in accordance with the manner in which the infrared image is enhanced, and to generate a converted color component image signal of each of the specific colors; and a processed image signal generator configured to generate the processed image signal on the basis of the plurality of converted color component image signals.