PROBLEM TO BE SOLVED: To accurately calculate similarity between a case of a query and other case.SOLUTION: When an image set similar to a search object image set which is a search object, is searched in a case image set group acquired by photographing by multi times, with a time interval for each patient, an image processing device 100 performs following processing of: identification of one or more sets including a set of images having a feature amount similar to a set of a feature amount of the first image and a feature amount of the second image, in a case image set group, for the set of the first image which is photographed at a first time and a second image photographed at a second time different from the first time, in the search object image set； and determination of similarity between the search object image set and one or more sets in the case image set group, using a feature amount of one or more images photographed at a time between a photographing time of a first similar image similar to the feature amount of the first image, and a photographing time of a second similar image similar to the feature amount of the second image, included in the identified one or more sets.SELECTED DRAWING: Figure 12
