The construction industry has lower levels of improvements in technology and productivity than any other industry. One of the most useful tools to change this state of affairs is construction automation. Steel frame fabrication is a major activity in building construction, but it is difficult to employ skilled labor, as the work is hard, dangerous, and specialized. Currently, there is pressure to develop an automation system for steel frame fabrication, and this should be based on a detailed motion study to determine the required function and degree of freedom. We have developed a work breakdown structure (WBS) and modified the therblig symbol system to analyze in detail the unit motions of steel fabrication. We evaluated each motion using therblig and an analytic hierarchy process from the viewpoints of specialization, difficulty, and danger, and evaluated the overriding motion requiring automation. We propose a concept design for an automation system for steel frame fabrication that will be very helpful in automating steel frame fabrication.