Blue light included in visible radiation emitted during arc welding has caused photoretinopathy in some cases. The extent of the hazard of blue light varies depending upon the welding method and conditions. Therefore, it is important to identify the level of blue light under various conditions. In this study, we experimentally evaluated the hazard of blue light emitted during tungsten inert gas welding and metal inert gas welding of a magnesium alloy. In addition to this, the protect performances for the blue light of flter plates compliant with the Japanese Industrial Standard (JIS) were also evaluated experimentally. In this study, the hazard level of blue light was evaluated by the effective blue light radiance defined in the American Conference of Governmental Industrial Hygienists Guidelines. The effective blue light radiance measured was in the range of 11-21 W/(cm2･sr). The effective blue light radiance was higher at higher welding currents than that in lower welding currents and differed based on the types of electrodes. It was suggested that the hazards caused by blue light emitted during arc welding of the magnesium alloy can be suffciently reduced by passing through an appropriate filter plate standardized by the JIS T 8141.