A data analysis device is configured to include an arithmetic operation device that determines whether or not each point data in the point data group of the existing clusters is a core of the cluster using a predetermined algorithm and calculates a predetermined re-verification determination data, recalculates an initial condition value of the clustering based on the re-verification determination data, specifies re-verification point data which is the point data that becomes no longer the core or becomes a new core by adding the point data, from the point data group to which the addition was made, based on the updated initial condition value obtained by the recalculation, and performs predetermined clustering processing in accordance with the re-verification point data.