To provide a positional information providing system capable of improving stability in transmitting a GPS signal.

A positional information providing system 1 is to provide a user in a room of a building with positional information using a GPS signal sent from a satellite and is arranged outside the building. The system comprises: a receiving antenna 10 to receive the GPS signal sent from the satellite; a transmitting antenna 70 which is arranged so as to allow a plane coordinate inside the building thereof to correspond to the plane coordinate of the receiving antenna 10 and sends the GPS signal received by the receiving antenna 10 to inside the building; and optical transmission means which connects the receiving antenna 10 and the transmission antenna 70 each other and transmits the GPS signal received by the receiving antenna 10 toward the transmission antenna 70 through optical communication.