Abstract: The apparatus for transporting and collecting self-propelled carriages for carrying out fillet welding of a construction in the rectangular form has carriages adapted to move along rails extending in the longitudinal direction which rails are in turn movable in the transverse direction, extension ladders each suspended by the respective carriages through rotating means so as to be rotatable about its longitudinal axis, clamp jaws each supported by the respective extension ladders. The clamp jaws are adapted to releasably clamp the respective self-propelled carriages so that the carriages are lifted and swivelled to assume orientation required for the fillet welding in the desired direction and again lowered and released from the clamp jaws thereby permitting the fillet welding of a construction in the rectangular form in different regions.