1. A tissue imaging system comprising: an imaging unit for creating an object image of an object with information of oxygen saturation of a blood vessel; an area determining unit for determining a specific area within said object image, said specific area being movable by following motion of said object; a monitor image generating unit for generating a monitor image including change information of said oxygen saturation according to a part image included in said object image and located in said specific area; and a display unit for displaying said monitor image.