PURPOSE: To calculate the loss of power in a rolling mill system that is used at the time of setting rolling schedule with high accuracy.

CONSTITUTION: In the case of calculation of the loss Lossi of power, test run of each rolling stand is plural times executed in the state of kiss-roll and data are collected to determine unknown coefficients C1i, C2i, C3i, in a prescribed operation expression including rolling force PRi and roll speed Vri. The values of C1i, C2i, C3i are determined by executing regression analysis of these data. After Ci, C2i, C3i are determined like this, the loss Lossi of power under a certain condition is calculated with a means 2 for calculating the loss of power by substituting desired values for PRi and VRi in the prescribed operation expression.