To provide an image acquisition device which has a wide-field and high resolution imaging optical system, and which quickly measures a cover glass thickness with a simple structure, in order to correct aberration fluctuation due to unevenness of the cover glass thickness.

An imaging device 100 for projecting an image of a sample held by a sample holding part 30, onto an imaging element 50 by an imaging optical system 40 comprises: thickness measuring means 601 for imaging the sample holding part from a direction intersecting with an optical axis of the imaging optical system, and on the basis of information obtained by the imaging, measuring a thickness of a transparent plate located on a side of the imaging optical system of the sample holding part; and correction means for, on the basis of the measurement result by the thickness measuring means, correcting at least one of aberration and focal position deviation caused by the transparent plate.