In order to estimate an appropriate shop time, the characteristics of waiting time must be revealed, and we have disclosed several estimation formulae. Using those formulae, we can estimate shop times easily, but there remains an important problem; that is, even if the average waiting time is reasonable or fairly short, there cartainly are some jobs with much longer waiting time. So, it is proposed to control the work load of the first stage of the process lest such a job should be created. In other words, newly arrived job should be rejected in the event that the work load, by accepting it, will exceed the limited value given. This control system is considered to be so-called finite queuing system, but we have investigated the characteristics by a convolutional numerical analysis.