A map updating system that includes a map database storing map data and performs update processing on the map database upon reception of update data, comprising: a memory having an update processing area used for the update processing and a cache area used as a cache; an update processing unit for performing the update processing by reading data required in the update processing from the cache area when the data are stored in the cache area and from the 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; and a navigation processing unit for performing predetermined navigation processing; characterized by a processing memory capacity determination unit for determining a processing memory capacity, which is a capacity of the memory required as the update processing area, on the basis of one or both of a number of roads and a number of intersections included in the map data to be subjected to the update processing; a navigation memory capacity determination unit for determining a navigation memory capacity, which is a capacity required as an area of the memory used in the navigation processing, on the basis of one or both of a type and a number of application processes that are underway as the navigation 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 and the navigation memory capacity; wherein the navigation memory capacity determination unit determines the capacity of the memory required to execute the application processing in relation to each of the application processes, obtains information relating to the execution state of each application process, and determines the navigation memory capacity on the basis of the total memory capacity required for the application processes that are underway. a memory having an update processing area used for the update processing and a cache area used as a cache; an update processing unit for performing the update processing by reading data required in the update processing from the cache area when the data are stored in the cache area and from the 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; and a navigation processing unit for performing predetermined navigation processing; characterized by a processing memory capacity determination unit for determining a processing memory capacity, which is a capacity of the memory required as the update processing area, on the basis of one or both of a number of roads and a number of intersections included in the map data to be subjected to the update processing; a navigation memory capacity determination unit for determining a navigation memory capacity, which is a capacity required as an area of the memory used in the navigation processing, on the basis of one or both of a type and a number of application processes that are underway as the navigation 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 and the navigation memory capacity; wherein the navigation memory capacity determination unit determines the capacity of the memory required to execute the application processing in relation to each of the application processes, obtains information relating to the execution state of each application process, and determines the navigation memory capacity on the basis of the total memory capacity required for the application processes that are underway.