Fixation of structural parts to concrete is a repetitive, heavy-duty, and time-consuming task that requires automation due to the lack of skilled construction workers. Previously developed automation techniques have not achieved the complete fixation of structural parts and are difficult to implement in narrow construction environments. In this study, we propose a construction robot system that enables the complete installation of structural parts to concrete and can be easily introduced to unstructured and narrow construction environments. The system includes two arms that simultaneously position and fix the structural parts, and custom tools that reduce the reaction force applied to the robots so that smaller robots can be used with lower payloads. Due to the modular design of the proposed system, it can be transported in parts for easy introduction to the construction environment. We also propose a procedure for fixing structural parts. Experimental results demonstrate that the custom tools make it possible to use smaller robots without moment overload in the robot joints. Moreover, the results show that the proposed robot system and fixation procedure enable automatic fixation of a structural part to concrete.