This study was performed to construct a new production system involving use of a fiber laser welding robot for welding of sheet metal parts of machine tools. Production technology with automation of the welding process is indispensable to produce competitive sheet metal parts, even in high-mix, low-volume production. On the other hand, robot welding requires a jig to temporarily assemble and fix multiple sub-parts. However, due to the problem of the number of jigs is increased too much, we are carrying out technical development for jig-less welding that combines laser conduction welding and mortise joint technology. In this report, we measured the heat input during welding in laser keyhole welding, laser conduction welding and manual welding, and investigated the relationship with welding strain. As a result, it is found that the introduction of laser robot welding can achieve improvement in productivity and accuracy, and the results are reported.