1. A measurement system comprising: a multi-articulated robot including a light receiving device at a front end of an arm; and a machine tool that is provided inside a range of operation of the robot and utilizes the light receiving device to measure a target fastened to the machine tool, wherein the target has a geometric feature enabling identification of information on a position of an image of the target formed on a light receiving surface of the light receiving device and information on a length relating to a distance between the light receiving device and the target, and the measurement system further comprises: a measurement position/posture determining part determining a plurality of stop positions of the machine tool and a plurality of measurement positions and postures of the robot whereby when the machine tool is at the plurality of stop positions, the target is included in a field of vision of the light receiving device, a positioning part successively positioning the machine tool at the plurality of stop positions and successively positioning the robot at the plurality of measurement positions and postures corresponding to the plurality of stop positions, a target detecting part forming the image of the target on the light receiving surface of the light receiving device and using information on the position of the target and information on the length as the basis to detect information on the distance between the light receiving device and the target, a robot moving part moving the robot so that in a state where the machine tool is at a stop position and the robot is at a measurement position and posture, a difference between a position of the target on the light receiving surface of the light receiving device and a predetermined location of the image acquired by the light receiving device becomes within a predetermined error and a difference of information on the distance and a predetermined value becomes within a predetermined error, a robot end point storing part storing positions and postures of the robot after being moved by the robot moving part as end points linked with the stop positions of the machine tool and the measurement positions and postures, and a calculating part using the plurality of end points corresponding to the plurality of stop positions and the plurality of measurement positions and postures and the plurality of stop positions as the basis to simultaneously find error of the mechanical parameters of the robot and a correspondence between the coordinate system of the robot and the coordinate system of the machine tool.