A device for measuring a position of a mobile station according to the present invention comprises: first measuring means for measuring the position of the mobile station based on observed data of signals from satellites using a one-epoch measuring method; second measuring means for measuring the position of the mobile station using previous determination result of the position of the mobile station and speed information representative of a speed of the mobile station; third measuring means for measuring the position of the mobile station using solutions of variables derived from previous determination results of the first or second measuring means; and controlling means 60 for selecting one of the respective measuring means which is to execute its measuring process; wherein if reliability of the determination result of the selected measuring means is lower than a predetermined reference value, the controlling means selects another measuring means to make it execute its measuring process.