1. A method, implemented by an electronic control unit in an camera calibrating apparatus, for calibrating multiple cameras installed on a vehicle, the method comprising: a first act of acquiring a two-dimensional image by imaging a reference pattern around the vehicle by using the multiple cameras installed on the vehicle, the reference pattern including multiple pattern pieces disposed on a road surface, each of the multiple pattern pieces having geometric shape with at least three sides, and having predetermined positional relationships with each other and predetermined original coordinates corresponding to points of the geometric shape, wherein each of the cameras image at least two of the multiple pattern pieces in the two-dimensional image of the reference pattern; a second act of performing, by the electronic control unit, coordinate conversion for converting coordinates of three or more points for each of the multiple pattern pieces of the reference pattern in the two-dimensional image to coordinates of an analyzed pattern, by combining a roll compensation and a bird's-eye conversion based on a depression angle and a roll angle of each of the multiple cameras, wherein an origin of the coordinates of the analyzed pattern after coordinate conversion is set to camera positions of each of the multiple cameras; a third act of determining, by the electronic control unit, the depression angle and the roll angle that minimize distortion of the analyzed pattern based on the converted coordinates of the analyzed pattern and the coordinates of the reference pattern to have the analyzed pattern resemble the geometric shape of the pattern piece, wherein the determination of the depression angle and the roll angle is performed by repeating the second act with the depression angle and the roll angle changed in repeating of the second act; a fourth act of calculating, by the electronic control unit, the coordinates of each of the camera positions in a coordinate system of the reference pattern on the road surface based on (a) calculation of a rotation angle of the camera in a horizontal direction for matching the analyzed pattern to relative positions of the multiple pattern pieces in the reference pattern and (b) calculation of the rotated coordinates of the analyzed pattern by the calculated rotation angle in the horizontal direction; and a fifth act of calculating, by the electronic control unit, the rotation angle of each of the cameras relative to the vehicle, based on (a) the rotation angle of the camera in the horizontal direction and (b) a relationship between (i) the coordinates of the camera position in a reference pattern coordinate system and (ii) the coordinates of the camera position in a vehicle coordinate system.