To efficiently acquire data and to facilitate comparative observation of a multitude of images by simplifying positioning work for an experimental small animal.

This fluorescence observation device 1 is equipped with: a display part 5 for displaying a plurality of composite images made by combining bright-field images of the experimental small animal A and its fluorescent images with them arranged at least in one direction; an outline extraction part 6 for extracting the outline shapes of the small animal A in the bright-field images included in the respective composite images; and an image position adjustment part 6 for adjusting the display positions of the respective composite images so that the outline shapes of the small animal A extracted by the extraction part 6 coincide with each other in a direction orthogonal to the arrangement direction.