This paper deals with a robotic system for the steel beam assembly task in building construction. Applying the robotic system on the steel beam assembly, we pursue such advantage as improving safety for workers and reducing construction period and cost. The robotic bolting device suggested in this paper has a gantry-type moving apparatus which includes a bolting end-effector. The bolting end-effector is designed especially for bolting mechanism using TS(Torque Shear) type bolt. In order to perform the bolting assembly tests, we made an experimental testbed which was similar to a real steel construction environment. Through the tests, we acquired feasible results for applying the robotic bolting device to real steel construction sites.