An upgrade method for navigation data is provided with: a memory status of
a memory device that is removed from a navigation apparatus is checked
and it is determined whether there are the navigation data to be upgraded
and the user data to be saved. The user data is saved in a backup memory
device. The navigation data is written over with upgraded navigation
data. Then, the saved data is read from the backup memory device and
rewritten in the memory device as the user data.