Abstract: This image acquisition apparatus includes a bottom surface position detection apparatus, and acquires an image of biological cells disposed in wells of a vessel. The bottom surface position detection apparatus includes a holder, a light irradiator, a detector, and a controller. The holder horizontally holds a vessel. The light irradiator irradiates a bottom portion of the vessel with a light beam. The detector detects a first reflected light beam reflected from a first bottom surface that is a bottom surface of the vessel and a second reflected light beam reflected from a second bottom surface that is a bottom surface of the wells. The controller calculates the position of the second bottom surface, based on a first peak position of the first reflected light beam and a second peak position of the second reflected light beam both detected by the detector.