An observation data screening unit (103) executes least squares method positioning using, as an observation amount, n (n is an integer of 3 or larger) number of single difference amounts of an L1-wave pseudorange obtained from n pieces of observation data from n number of positioning satellites and n pieces of correction data corresponding to the n pieces of the observation data. The observation data screening unit (103) calculates a sum of squares of n residuals obtained for each positioning satellite by executing the least squares method positioning and normalizes the n residuals. The observation data screening unit (103) then evaluates the sum of squares of the residuals and the n normalized residuals.