A measuring system which can easily measure a three-dimensional position of a target to be measured using a light receiving device mounted to a manipulator of a robot. When the manipulator is positioned at a first position, a moving process for moving an image of the target imaged by the light receiving device or a camera to a center of a light receiving surface of the camera is executed. Next, the manipulator positioned at the first position is moved, without changing the orientation of the camera, to a second position where the distance between the camera and the target is different to that at the first position. After that, the moving process is executed again. Based on the position of the manipulator after the process, the orientation of a coordinate system .SIGMA.v1 representing the direction of a visual line is calculated. Then, the manipulator is rotated by 180 degree about Z-axis of the coordinate system .SIGMA.v1 and the moving process is executed again. A middle point of the positions of coordinate system .SIGMA.v1 before and after movement of the manipulator is determined as an origin of a coordinate system .SIGMA.v2 representing the orientation and the position of the visual line. The manipulator is inclined relative to Y-axis of the coordinate system .SIGMA.v2 and the moving process is executed again, so as to calculate the three-dimensional position of the target.