I. Introduction
In recent years, assembly tasks at factories are one of the areas where automation by robot is most prosperous [1] [2]. Currently, a wide range of assembly tasks have been automated, e.g., mounting of rotary equipment on turbo chargers of the car, and assembling of main wings of the aircraft. However, tasks that have been put into practice at this moment are limited to those that are highly reproducible and are constituted by a series of simple actions. At factories, there are many tasks with lower reproducibility due to their complexity and stringent success conditions. Therefore, it is difficult to automate complex tasks at factories; such complex tasks are now being carried out by human hands.