A guidance assistance system and the like for reducing an influence on a deviation of a crowd from a travel route are provided.The guidance assistance system includes deviation risk evaluation means for deriving a deviation risk representing an influence on a deviation of a crowd from a travel route at a predetermined point on the travel route based on information relating to circumstances of the travel route and a route related to the travel route, and priority order determining means for determining an order of priority relating to arrangement of a guide sign that guides the crowd based on the deviation risk.