Observation device

An observation device comprising:

• a stereo image-acquisition optical system that acquires images of cells floating in a culture fluid inside a culture vessel;
• and
• an analyzer that calculates a cell density of the cells on the basis of the images acquired by the stereo image-acquisition optical system,
• wherein the analyzer identifies a three-dimensional position of each of the cells included in the images and calculates the cell density on the basis of the number of cells present within a predetermined three-dimensional region,
• wherein the stereo image-acquisition optical system comprises:
• a stereo optical system that forms, for the same cell floating in the culture fluid, two views with parallax due to being viewed from different viewpoints;
• and
• an imager that acquires images of the two views formed by the stereo optical system,
• wherein the stereo optical system comprises:
• an objective optical system that comprises lenses and that focuses light from the cells;
• and
• an aperture opening that splits the light focused by the objective optical system,
• wherein the aperture opening includes a first opening and a second opening, and
• wherein the imager acquires images of light that passes through the first opening and the second opening respectively as the images of the two views, the images of the two views being acquired from the same observation position at the same time.