Abstract: An articulated robot such as an arc welding robot includes a plurality of articulations and an end effector having a tool center point. To teach the robot, a coordinate transformation matrix for transforming coordinates between the articulations is determined from condition data of the articulations. A present position of the tool center point is calculated based on the coordinate transformation matrix and a moving vector is determined from the present position of the tool center point to a next position thereof. Thereafter, a new coordinate transformation matrix for transforming coordinates between the articulations is determined so that the posture of the end effector at the next position of the tool center point, which is calculated based on the first-mentioned coordinate transformation matrix and the moving vector, will coincide with the posture of the end effector at the present position of the tool center point.