Laser-arc hybrid welding is divided into laser-based and arc-based welding. In the arc-based welding, the laser beam irradiation provides the guiding effect of the arc plasma. Some studies have reported that an unstable arc plasma becomes stable due to this guiding effect. This is considered as the influence of metal vapor generation by laser beam irradiation, however, there are few reports on the measurement of metal vapor and arc plasma state during the guiding process. Therefore, the mechanism has been still not fully understood. In this study, the fundamental study of the guiding arc phenomenon was conducted in TIG arc welding (60A) with laser beam irradiation (170W) under relatively low power condition. When the base metal was stainless steel, the guiding arc by the laser beam irradiation was observed unlike the mild steel. Spectroscopic measurement for the guiding arc phenomenon in stainless steel showed that the metal vapor was composed of manganese and chromium, and was widely distributed near the irradiation point, but not concentrated. We also observed the decrement of plasma temperature, which is considered to be caused by distributed metal vapor and the resultant decrement of the current density.