Hydraulic excavators 1 working in fields each include a controller 2, and an operating time is measured for each of an engine 32, a front 15, a swing body 13 and a track body 12. The measured data is stored in a memory of the controller 2, transferred to a base station computer 3 through satellite communication, an FD, etc., and stored in a database 100 of the base station computer 3. In the base station computer 3, the data stored in the database 100 is read out for each of the hydraulic excavators to obtain a value of an index (e.g., a travel ratio) regarding the state of use of a particular one of the hydraulic excavators and a distribution of the number of operated hydraulic excavators of the same model as the particular hydraulic excavator with respect to the index. The index value and that distribution are compared with each other to determine whether the particular hydraulic excavator is an optimum model. It is therefore possible to make an evaluation after confirming how a customer employs a machine, and to give an advice about the optimum model depending on the state of use of the machines.