1. An image obtaining apparatus, comprising: a light source configured to irradiate a biological sample having a fluorescent label with excitation light, the excitation light exciting the fluorescent label; an optical system including an objective lens, the objective lens being configured to magnify an imaging target of the biological sample; an image sensor configured to form an image of the imaging target magnified by the objective lens; a movement controller configured to move a focus position of the optical system in an imaging range including at least a range corresponding to the thickness of the imaging target; and a data processing unit configured to exposure the image sensor to light while moving the focus position in the imaging range and obtain a fluorescent image of the biological sample, to thereby calculate distribution information of the fluorescent label in a thickness direction of the imaging target based on the fluorescent image.