A navigation apparatus comprising: map data storage means for storing map data; writing-reading means for writing the map data into a portable storage medium and for reading out the map data from the portable storage medium; capacity detection means (13, 19) for detecting a maximum storage capacity of the portable storage medium; central coordinates inputting means for inputting a coordinates position of a central geographic point of the map data to be written into the portable storage medium; sectional region setting means for setting a central sectional region with a predetermined range centering on the central geographic point and sequentially setting at least one outer sectional region surrounding the outside of the central sectional region at a predetermined distance interval; extracting-region creating means for sequentially creating a map data extracting-region by sequentially adding the outer sectional regions or regions to the central sectional region; capacity judgment means for sequentially extracting map data of the map data extracting-region created by the extracting-region creating means from the map data storage means and for sequentially judging whether or not the storage capacity of the map data of the map data extracting-region is equal to or less than the maximum storage capacity; storage region determination means for determining the largest map data extracting-region which does not exceed the maximum storage capacity as map region to be stored in case the capacity judgment means judged that the map data of the map data extracting-region has exceeded the maximum storage capacity; and writing control means for extracting the map data of the map region to be stored from the map data storage means and for controlling to write into the portable storage medium through the writing-reading means the map data of the map region to be stored. map data storage means for storing map data; writing-reading means for writing the map data into a portable storage medium and for reading out the map data from the portable storage medium; capacity detection means (13, 19) for detecting a maximum storage capacity of the portable storage medium; central coordinates inputting means for inputting a coordinates position of a central geographic point of the map data to be written into the portable storage medium; sectional region setting means for setting a central sectional region with a predetermined range centering on the central geographic point and sequentially setting at least one outer sectional region surrounding the outside of the central sectional region at a predetermined distance interval; extracting-region creating means for sequentially creating a map data extracting-region by sequentially adding the outer sectional regions or regions to the central sectional region; capacity judgment means for sequentially extracting map data of the map data extracting-region created by the extracting-region creating means from the map data storage means and for sequentially judging whether or not the storage capacity of the map data of the map data extracting-region is equal to or less than the maximum storage capacity; storage region determination means for determining the largest map data extracting-region which does not exceed the maximum storage capacity as map region to be stored in case the capacity judgment means judged that the map data of the map data extracting-region has exceeded the maximum storage capacity; and writing control means for extracting the map data of the map region to be stored from the map data storage means and for controlling to write into the portable storage medium through the writing-reading means the map data of the map region to be stored.