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 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 an image signal processing circuit for generating 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 that is output by the solid-state image sensor and is 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 performs: a component image signal generation process for generating an infrared component image signal that corresponds to an infrared light component, and generating 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 process for synthesizing, 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 generating a converted color component image signal of each of the specific colors; and a processed image signal generation process for generating the processed image signal on the basis of the plurality of converted color component image signals.