If a lesion included in a specification target image is a texture lesion, a probability image calculation unit calculates a probability value indicating a probability that each of a plurality of pixels of the specification target image is included in a lesion area. An output unit calculates, as a candidate area, an area including pixels whose probability values are equal to or larger than a first threshold in a probability image obtained from the probability image calculation unit and, as a modification area, an area including pixels whose probability values are within a certain probability range including the first threshold. An input unit detects an input from a user on a pixel in the modification area. A lesion area specification unit specifies a lesion area on the basis of the probability image, the candidate area, the modification area, and user operation information.