Abstract: A building structural material produced by A magnesium alloy contains aluminum in a range of 0.1 wt % to 1.0 wt %, zinc in a range of 0.1 wt % to 2.0 wt %, manganese in a range of 0.1 wt % to 1.0 wt %, 0.04 wt % or less copper, 0.05 wt % or less silicon, 0.005 wt % or less iron, and 0.005 wt % or less nickel. This building structural material had no cracks even when it was extruded at an extrusion speed about ten times as high as the conventional speed and also no ignition attributable to surface oxidation occurred.