1. An image processing device comprising: an input unit to input a bright field image of a tissue slice in which a cell nucleus is stained and a fluorescent image of the tissue slice in which a specific biological substance is stained with a fluorescent staining reagent; a first extracting unit to extract a cell nucleus from the bright field image; a second extracting unit to extract a fluorescent bright point from the fluorescent image; an assigning unit to specify a cell nucleus to which the fluorescent bright point is assigned on the basis of a distance between the cell nucleus and the fluorescent bright point and to assign. the fluorescent bright point to the cell nucleus; and an excluding unit to exclude a fluorescent bright point after assignment processing from the assigned fluorescent bright points on the basis of an average distance between a surface of the cell nucleus and the fluorescent bright point after assignment processing, inclination or angle between straight lines connecting the fluorescent bright points after assignment processing, or the N/C ratio of the cell to which the fluorescent bright point is assigned.