A map updating system includes: an update processing unit for performing update processing by reading data required in the update processing from a cache area of a memory when the data are stored in the cache area and from a map database when the data are not stored in the cache area; a cache storage unit for storing the data read by the update processing unit in the cache area; a processing memory capacity determination unit for determining a processing memory capacity, which is a capacity of the memory required as an update processing area, on the basis of the content of map data to be subjected to the update processing; and a cache capacity determination unit for determining a cache capacity, which is a capacity of the memory allocated to the cache area, on the basis of the processing memory capacity.