1. A calculation device comprising: a memory; and a processor coupled to the memory and configured to: identify a person in a plurality of images captured in time series respectively, obtain gaze information indicating a direction of a line of sight of the person, identify at least one of a time period in which the person directs the line of sight to a certain object and a number of times that the person directs the line of sight to the certain object, based on the gaze information and a position at which the certain object is placed, estimate a relationship of two or more persons who are identified in one image from among the plurality of images, based on a distance between the two or more persons, and calculate an index value indicating probability that the certain object is utilized, based on the relationship, and at least one of the time period and the number of times.