1. A vacuum-processing method of carrying out, in a vacuum processing vessel, a process wherein a condition of an interior of the processing vessel changes as the number of processed objects increases, and controlling a controlled parameter affecting an effect of the process directly so that the controlled parameter is maintained at a target value, said vacuum-processing method comprising the steps of: determining a model function obeying a change of the condition of the interior of the processing vessel; and calculating the target value of the controlled parameter every time one or a plurality of objects are processed, on the basis of the model function and a set value of a set parameter representing the effect of the process.