A navigation apparatus includes hierarchically road map data having third-, second-, and first-layer data respectively representing a high, intermediate, and low road rank. The layer data are contiguously disposed in a storage portion in the order of the road ranks. The first- and second-layer data include area data about individual zones into which a region corresponding to the third-layer data is divided. According to a read request designating a bunch of area data, a cached portion of the designated bunch of area data is obtained from a cache area. The remaining portion is obtained from the storage portion such that an address range of the storage portion from the start point to the end point of the remaining portion is collectively read while area data not designated by the read request but positioned between the remaining portion are additionally read.