An on-board navigation apparatus is designed to shorten the time for a display operation at the time of displaying a map and scrolling a screen while employing a buffer memory with a smaller memory capacity. The apparatus reads only block data of a block containing a display center point and block data of blocks adjoining thereto and stores the data into a buffer memory, and acquires display data forming a display screen with the display center point as a reference point from the buffer memory and performs a display operation. The reading/storing operation includes an operation of storing the block containing the display center point and blocks adjoining thereto separately into the buffer memory. The display control operation includes an operation of temporarily storing the display data into a display buffer memory before displaying it.