24 under control of the cpu 22 on the basis of the updated data 300 generated at the step s 14 see fig8 that is only with the node data 110 or link data 120 included in the updated data 300 the navigation processing is proceeded then the process goes to the step s 25 on the other hand if the data storing the node or link that the cpu accesses next is included in the difference update data 400 step s 21 yes among from the difference update data 400 stored in the cd rom 33 the dvd rom 34 or the hard disk 36 the node data 110 or link data 120 to be accessed next is read and stored into the ram 24 step s 22 then the navigation processing is proceeded step s 23 under control of the cpu 22 on the basis of the updated data 300 generated at the step s 14 see fig8 and the node data 110 or link data 120 in the difference update data 400 that is read at the step s 22 that is with node data 110 or link data 120 included in the updated data 300 and node data 110 or link data 120 included in the difference update data 400 the navigation processing is proceeded then it is judged whether or not the node or link to be accessed next in the navigation processing exists.