Apparatus for determining a positioning error includes: database for storing grid cells separated by each pCell ID and WLAN environment information matched to grid cells; information receiving unit for receiving terminal WLAN environment information from mobile communication terminal; identification information checking unit for checking AP identification information included in terminal WLAN environment information; triangulating unit for calculating triangulation coordinate value by performing triangulation with AP position estimation information corresponding to AP identification information; grid cell positioning unit for selecting one or more grid cells corresponding to AP identification information and calculating grid cell coordinate value based on coordinate value corresponding to grid cell selected; and error determining unit for comparing triangulation coordinate value and grid cell coordinate value and determining whether there is positioning error in any one of triangulation coordinate value and grid cell coordinate value.