To quickly optimize processing distribution in an assembly line without depending on the individual difference of a manager by obtaining predicted work time from a time change coefficient established between work difficulty levels and skill levels and balancing allocated work time per person among respective workers.

The difficulty levels of the respective element works of assembly-line work and the skill levels of the respective workers to be fed are respectively ranked and the time change coefficient is set based on them. Then the matrix of the decided difficulty levels A-C and skill levels 1-3 is prepared and the time change coefficient at the time of performing the individual element works is allocated for the individual workers. Thus, the predicted work time for which the skill level of the worker and the difficulty level of the work are included in the elements of optimum distribution is computed. By allocating the respective element works to the respective workers so as to balance the allocated work time per person for the predicted work time among the respective workers based on the computed predicted work time, the work time of the respective workers is uniformized with minimum work time.