When the process plan made for execution is corrected based on the process correction condition, the variation amount in each of processes based on the process correction condition is calculated as the probability distribution using the probability distribution data generated by obtaining the probability distribution from the variation-amount prediction value of each of the processes. Thereby, the influence degree on other processes when the process is corrected can be estimated not simply as the propagation of the variation fixed value but so as to be more suited to the actual circumstances in accordance with the attribute information and the past variation patterns of the process.