A storage section (160) stores a traffic jam prediction table containing a plurality of date classification IDs for classifying data for predetermined dates and time series data obtained by statistically processing past traffic conditions correlated to the date classification IDs in terms of temporal elements of the dates. A memory (170) stores calendar templates, each containing a plurality of pieces of date information and classification ID numbers, each of which is an ID number that corresponds to the date indicated by one of the pieces of date information and is same as one of the date classification IDs of the traffic jam prediction table. A navigation device (100) has a calendar modifier that appropriately modifies any of the classification ID numbers of the calendar templates.