An image acquisition device for acquiring an image of samples held on slide glasses, the image acquisition device comprising: 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, wherein the cassette mounting unit comprises a rotation drum including a bottom plate , a top plate , a plurality of cassette holding plates disposed between the bottom plate and the top plate to define a plurality of holding spaces (S), and a strut serving as a non-rotating shaft and provided between a central portion of the top plate and a central portion of the bottom plate ; a light source configured to emit inspection light toward the cassette mounted in the cassette mounting unit ; a scanning unit configured to perform scanning with the inspection light in the arrangement direction; a light reflection unit that is disposed on a side surface of the strut to face the light source and configured to reflect the inspection light emitted from the light source ; a light detection unit configured to detect reflected light including the inspection light reflected by at least one of the light reflection unit , the cassette , and the slide glass, and configured to output a detection signal; and an information generation unit configured to generate holding information on at least one of a holding position and a holding state of the slide glass held in the cassette on the basis of the detection signal, wherein the rotation drum is rotatable around the strut , and can be stopped at a position at which a holding space is located between the light source and the light reflection unit . 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, wherein the cassette mounting unit comprises a rotation drum including a bottom plate , a top plate , a plurality of cassette holding plates disposed between the bottom plate and the top plate to define a plurality of holding spaces (S), and a strut serving as a non-rotating shaft and provided between a central portion of the top plate and a central portion of the bottom plate ; a light source configured to emit inspection light toward the cassette mounted in the cassette mounting unit ; a scanning unit configured to perform scanning with the inspection light in the arrangement direction; a light reflection unit that is disposed on a side surface of the strut to face the light source and configured to reflect the inspection light emitted from the light source ; a light detection unit configured to detect reflected light including the inspection light reflected by at least one of the light reflection unit , the cassette , and the slide glass, and configured to output a detection signal; and an information generation unit configured to generate holding information on at least one of a holding position and a holding state of the slide glass held in the cassette on the basis of the detection signal, wherein the rotation drum is rotatable around the strut , and can be stopped at a position at which a holding space is located between the light source and the light reflection unit . <EOS>