A method for correcting reference position information is provided. A reference position information correction judging section 62 of an assistance server 50 saves location information in a location information storage and saving section 65, and judges whether to perform a correction of reference position information. The location information corresponds to a location of a cellular phone 20 in a range cell 90. Next, a reference position information correcting section 63 calculates a corrected reference position 92 based on the location information for the range cell 90 stored in the location information storage and saving section 65. The corrected reference position 92 is sent to a database section 64 from the reference position information correcting section 63, and is set as the reference position information of the range cell 90.