The index scan device acquires information on a search space in a multi-dimensional space corresponding to a search range of a query; sets, as a search point, a data point corresponding to at least one of a minimum and a maximum of values obtained by changing each data point in the multi-dimensional space to be one-dimensional, from among data points contained in the search space or the partial search space; identifies index data associated with a partial space containing the search point; estimates a boundary line passing through the search space on the basis of identification information on the partial space obtained from the identified index data; and determines, from among divided search spaces obtained by dividing the search space by the estimated boundary line.