1. A teaching device for teaching a robot of positions for performing an operation on an object, comprising: storage means storing positional relation between of the robot and the object; first displaying means for displaying a model of the robot on a display device movable around the object with an operator; specifying means for the operator to specify a direction of a present position of the operator with respect to the robot, referring to the model of the robot displayed on the display device; second displaying means for displaying a three-dimensional model of the object as viewed from the specified direction of the operator on the display device; and manual operation means for the operator to operate the robot for designating positions for performing the operation on the object, referring to the three-dimensional model of the object displayed on the display device.