as make it execute the processing according to the present invention note that the program of the present invention may be received from another computer and held furthermore in fig2 the accumulated operating time of each pc measured since the initiation of the operation t 0 by the operating time measuring means 3 of the administrative server s is shown in a graph the axis of abscissa represents an leased or rented operating time time t from the initiation of the operation t 0 to the expiry of the operation time and the axis of ordinate represents the accumulated operating time of each pc the administrative server s determines combinations of candidates for rotation among the pc 1 to pc 5 at time tx after a certain time of time t 0 has elapsed within the leased or rented operation time time t when the operating times of the respective pcs needs to be averaged based on their accumulated operating times during the certain time of time t 0 this decision is made through a statistical process at the control means 1 of the administrative server s and the utilization tendency within the certain time time t 0 the magnitude of the accumulated operation time at the time tx a future utilization plan and the like are taken into consideration for example to look at the pc 1 the accumulated operating time becomes long to some extent at the time tx the utilization time drastically.