Abstract: A laser beam processing robot having a multi-joint arm assembly includes a main body, which is provided to be movable along a predetermined straight line, and a multi-joint arm assembly mounted on the main body. The assembly includes a first arm which is rotatably coupled to its base portion through a first joint, which, in turn, is fixedly mounted on the main body. The assembly also includes an optical system which defines an optical path for a laser beam. The first joint is provided with a first through-hole which extends in parallel with the predetermined straight line and through which a laser beam supplied from a source is passed to be guided into the optical path of the assembly. Moreover, optical elements of the optical system are arranged on both sides of the assembly so that repair and maintenance of the optical system is facilitated.