Abstract: A working time for each of an engine 32, a front 15, a swing body 13, and a travel body 12 of a hydraulic excavator 1 working in fields is measured. Measured data is stored in a memory of a controller 2 and then transferred to a base station computer 3 via satellite communication, an FD, etc. to be stored in a database 100. At each repair/replacement of a part in each hydraulic excavator, the base station computer 3 calculates, based on the operation data, a replacement time interval of the part on the basis of the working time per section to which the part belongs, and then stores and accumulates it. The base station computer also reads the stored data for each hydraulic excavator, determines, for each part, a replacement rate of the part having the substantially equal replacement time interval, and calculates a target replacement time interval of the part in accordance with the replacement time interval corresponding to a maximum replacement rate.