To make the accuracy higher in calculating the moving distance of a moving body with a simple constitution.

A moving distance calculating device first acquires the positional information on a series of vehicles detected at every prescribed sampling time interval (S50). Then, the device extracts a plurality of groups of positional information changed in a sampling time interval from the acquired series of positional information by fetching the positional information at every prescribed bit of positional information and calculates the straight moving distances of the vehicles from each group of positional information (S52 and S54). In addition, the device finds the approximate expression of the moving distances using the sampling time interval as a variable based on the straight moving distances (S62). Furthermore, the deice calculates the moving distance by substituting a time interval 0 for the variable of the approximation expression (S62). Through the above-mentioned processing, the moving distance of the moving body can be found more accurately.