A fluorescence observation apparatus comprising: an image storage unit configured to store a plurality of pairs of bright-field images and fluorescence images of a small laboratory animal in such a manner that relative positions thereof are associated; a display unit configured to display the pairs of bright-field images and fluorescence images such that the images are arrayed in at least one direction or displayed in a switching manner; and an outline extracting unit configured to extract an outline shape of the small laboratory animal in each bright-field image; characterized by further comprising: an image-position adjusting unit configured to calculate longitudinal axes directions and orientations of the longitudinal axes of the outline shapes of the small laboratory animal, and to adjust a display angle of each bright-field image and associated fluorescence image so that the outline shapes of the small laboratory animal extracted from the bright-field images by the outline extracting unit are aligned, wherein the image-position adjusting unit further is adapted to calculate centers of gravity of the outline shapes of the small laboratory animal and to adjust the display position of the bright-field images and the associated fluorescence images so that the centers of gravity of outline images extracted by the outline extracting unit are aligned with each other. an image storage unit configured to store a plurality of pairs of bright-field images and fluorescence images of a small laboratory animal in such a manner that relative positions thereof are associated; a display unit configured to display the pairs of bright-field images and fluorescence images such that the images are arrayed in at least one direction or displayed in a switching manner; and an outline extracting unit configured to extract an outline shape of the small laboratory animal in each bright-field image; characterized by further comprising: an image-position adjusting unit configured to calculate longitudinal axes directions and orientations of the longitudinal axes of the outline shapes of the small laboratory animal, and to adjust a display angle of each bright-field image and associated fluorescence image so that the outline shapes of the small laboratory animal extracted from the bright-field images by the outline extracting unit are aligned, wherein the image-position adjusting unit further is adapted to calculate centers of gravity of the outline shapes of the small laboratory animal and to adjust the display position of the bright-field images and the associated fluorescence images so that the centers of gravity of outline images extracted by the outline extracting unit are aligned with each other. an image-position adjusting unit configured to calculate longitudinal axes directions and orientations of the longitudinal axes of the outline shapes of the small laboratory animal, and to adjust a display angle of each bright-field image and associated fluorescence image so that the outline shapes of the small laboratory animal extracted from the bright-field images by the outline extracting unit are aligned, wherein the image-position adjusting unit further is adapted to calculate centers of gravity of the outline shapes of the small laboratory animal and to adjust the display position of the bright-field images and the associated fluorescence images so that the centers of gravity of outline images extracted by the outline extracting unit are aligned with each other.