To favorably process time-serial load data.

Information as to loads is extracted in a wheel load extracting means 45, based on time-serial wheel load data, and distance series wheel load data arranged in order with the information included are generated thereafter. In the distance series load data, a data volume is reduced by the extraction of the information, and a calculation source is saved when the data is processed afterwards. The information as to the loads in every prescribed rotation of a wheel, i.e., the distance-serial data as to the loads with respect to a travel distance is brought by arraying the information about the loads in order, and the distance series load data includes no revolution speed of the wheel, i.e., no element of a travel speed in a rolling stock. Data processing for the distance series load data is conducted without taking the travel speed of the rolling stock into account.