1. A calculation device comprising: a memory; and a processor coupled to the memory and configured to: identify a first 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, the gaze information being obtained by calculating a gaze vector of the person and calculating a gaze position of the person based on the calculated gaze vector, 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, determine a distance between the first person and one or more second persons who are identified in at least one image from among the plurality of images, and determine whether there is a high probability that the first person and the one or more second persons have a human relationship based on the distance between the first person and the one or more second persons, and calculate an index value indicating probability that the certain object is utilized, based on whether there is a high probability that the first person and the one or more second persons have a human relationship, and at least one of the time period and the number of times.