A GPS positioning system including: a storage unit for storing therein assist data for GPS positioning; a determination unit for determining whether the stored assist data stored in the storage unit is valid or invalid; an autonomous positioning unit for, when the stored assist data is determined to be valid, based on the stored assist data determined to be valid without communicating with a base station, performing GPS positioning; an A-GPS positioning unit for, when the stored assist data is determined to be invalid, based on assist data acquired by communication with the base station, performing GPS positioning; and an updating unit for, when the GPS positioning succeeds, based on a result of the positioning, updating the stored assist data and, when the GPS positioning fails, based on the assist data acquired by communication with the base station, updating the stored assist data.
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