Korean War, ROK (Republic of Korea) Army Headquarters sleeve badge.

Hand-worked bullion on wool officer's or dress-quality piece rather than a standard issue patch, 

The ROK Army's own website describes the design, and every element matches this badge. The triangle represents the "three thousand ri" homeland, and the blue stands for peace. The triangular border symbolises guarding the nation's territory. The three small stars stand for the three ideals of national defence, unification and prosperity, and also for the three parts of a nation: its people, territory and sovereignty. The large star represents the army as the central force of national defence. Wikimedia also lists this as a Republic of Korea Army Headquarters insignia, credited to the ROK Army, which supports the identification.