1. An imaging apparatus, comprising: a light source device; an image pickup device for converting a living body observed image to video signals by using light irradiated from the light source device for observation; and a processor for generating a living body image from the video signals, the processor including means for generating a living body image having at least a scattering feature of a relative scattering change representing a degree of nucleus variant and structure variant of a living body tissue as image information, and the light source device irradiates a plurality of band light beams that exist in a band positioned as blue light in a visual light wavelength range, wherein the processor generates the living body image based on narrow band images obtained in synchronization with each irradiation of the plurality of band light beams and on an optical model corresponding to a particle size distribution of the living body tissue.