An operation management center divides an operation area in which an on-demand bus operates into a plurality of predetermined sub-areas, and searches for candidate routes on which the on-demand bus travels for each divided sub-area. The center sets one of the retrieved routes as a basic route, and sets, as adjustment time for each divided sub-area, time required when the bus passes through a location separated from the basic route. Thus, by setting such adjustment time for each sub-area, and by using the adjustment time set for each sub-area, the center can determine an operation plan that takes into account an additional request while reducing an impact on the determined operation plan.