Which Japanese foreign minister signed the Instrument of Surrender for Japan's government?

Mamoru Shigemitsu signed the Japanese Instrument of Surrender for Japan's government.

Shigemitsu signed first aboard USS Missouri on September 2, 1945, writing that he acted by command and on behalf of the Emperor of Japan and the Japanese government. General Yoshijirō Umezu signed separately for Imperial General Headquarters.

This division of signatures is an important detail. Shigemitsu represented the civilian government, while Umezu represented Japan's military headquarters. The two men were the only Japanese representatives who actually signed the instrument, although nine additional Japanese delegates attended the ceremony.

Shigemitsu had previously served as Japan's foreign minister and had signed the surrender documents despite having lost a leg in an earlier wartime attack. After the ceremony, the instrument was signed by representatives of the United States, China, the United Kingdom, the Soviet Union, and six other Allied nations.