We propose a method to estimate the self-position from the distance between the poles and the LiDAR-equipped robot by placing poles with known coordinates at the four corners of the map. This method can be used for self-position estimation outdoors, where the scan data acquired by LiDAR is not fixed in time and position. Although it is possible to perform self-position estimation if at least two poles are used, we prove that using four poles improves the maximum error of x-coordinate by 41% and y-coordinate by 83%. We also prove that the maximum distance error from the true value can be reduced to 3.2 cm.