An imaging system 100 for imaging a sample in a medium carried in a container WP as an imaging object comprises: an imager 21 which obtains an original image by imaging the imaging object; and a data processor 33 which generates multi-gradation image data by performing a gradation correction on the original image, wherein the data processor 33 associates a luminance value corresponding to a luminance of the medium in the original image with a maximum gradation value in the gradation correction.