PURPOSE: To attain an accurate correcting processing by converting a correction data extracted from a multidata into an RTCM1 type correction data in correspondance with a satellite orbit information extracted from a satellite signal and correcting a measuring information based on the correction data.

CONSTITUTION: An orbit data IODE of a receiving satellite received by a D GPS receiver 43 is extracted by a GPS.IOD extracting part 40 in a DARC to RTCM convertor 34 and the result is given to a differential correction computation part 39. In addition, a psuedo distance correction value PRC and distance change rate correction value RRC are sent to the part 39 through a differential data extracting part 35, PRC extracting part 36 and RRC extracting part 37. The part 39 calculated a differential correction value with an RTCM1 type format based on them and gives the result to a differential data CPU 46 so as to correct the measured position of a position measuring CPU 45. Thus an accurate correction can be made at all times.