An image acquisition device is an image acquisition device for acquiring an image of samples held on slide glasses and includes a cassette mounting unit in which a cassette is detachably mounted, the cassette holding the slide glasses in a plurality of stages in a predetermined arrangement direction, a distance sensor that measures a distance to the cassette mounted in the cassette mounting unit and outputs a detection signal based on a measurement result, and an information generation unit that generates state information on a mounting state of the cassette mounted in the cassette mounting unit on the basis of the detection signal.