We have developed a co-worker robot PaDY that delivers the parts and tools to workers at the appropriate timing by predicting the trajectory and task of a worker in the assembly process of a factory. Conventional PaDY works according to the worker on the premise that the worker understands the next task. If PaDY escorts a beginner worker, efficiency of work time and reduction of work errors can be expected. In addition, since the robot moves in front of the worker and the worker can receive the parts while moving, work efficiency can be improved for the skilled worker too. In order for PaDY to notify the worker of the next task and to escort the worker, it is necessary to always set the delivery position at a position that the worker can easily recognize and reach. Therefore, in this paper, we propose a method of determining the appropriate position for escorting workers while delivering the parts as the first step of the motion planning of escorting PaDY. Arm comfort, Collision, Manipulability, and Visibility were considered to determine the delivery position. In order to evaluate the reachability of worker's arm, a 6-DOF model of the worker's arm was created. In order to consider the worker's visibility, the participants' field of view was measured.