<p>Iwabitsu Castle Ruins in Higashi-Agatsuma-machi, Agatsuma-gun, Gunma Prefecture, is famous as mountaintop castle built by the Sanada clan in the Sengoku period, Japan. Two crucibles and four copper ingots excavated from the main bailey were investigated by non-destructive analysis using X-ray Radiography and X-ray Fluorescence Spectroscopy (XRF). As a result, we were found that one of the two crucibles was used for melting gold and another for melting bronze. As there were no impurities around the gold particle that could have been derived from gold ore, this consequence indicates that at placer gold was used. And, ingot’s materials were showed that three were bronze and one was pure copper by XRF. Also, adhesion of zinc was detected on all crucibles and one bronze ingot. In the crucible, zinc was attached in dots, and copper was not strongly detected in the same point. On the other hand, bronze ingot was showed that zinc was diffusely adhered. These results are suggested that brass was made from zinc metal or zinc mineral at the metal workshop where crucibles and copper ingots were used at that time. Therefore, we reveal that the existence of metal workshop utilizing gold and copper alloys such as bronze and brass in the main bailey of a mountaintop castle in the Sengoku period, for the first time in Japan.</p>