There have been built a large number of high-rise buildings equipped with facades (curtain-walls) in modern cities. These facades must be periodically maintained with manual procedures that are costly and risky. For this reason, the interest in developing and employing service robots for the building wall maintenance has been increased. Automation and robotics technologies allow safe and environmentally friendly facade cleaning, monitoring, and painting, which also reduce the cost of these tasks. These systems resolve the current safety problems associated with difficult and dangerous access, contributing to a zero injury and fatality in working performance. This paper deals with developing a Building Wall Maintenance Robot (BWMR) system based on a guide rail built in curtain-wall. The robot consists of both of horizontal and vertical units. The horizontal unit performs the maintenance works and is carried up and down by the vertical unit. The robot is designed to be fully automatic unlike other existing similar types of maintenance systems. Its feasibility has been verified through the experiments with down-sized robot and lab-scale building façade.