What was the formal title of the document that legally recorded Japan’s surrender in 1945?

The formal document recording Japan’s surrender was the Japanese Instrument of Surrender.

Representatives of Japan and the Allied powers signed it on 2 September 1945 aboard USS Missouri in Tokyo Bay. The document stated that Japan accepted the provisions of the Potsdam Declaration and ordered Japanese forces to cease resistance and surrender.

Mamoru Shigemitsu signed for the Japanese government, and General Yoshijirō Umezu signed for Imperial General Headquarters. Douglas MacArthur then signed for the Allied powers, followed by representatives from the United States, China, the United Kingdom, the Soviet Union, Australia, Canada, France, the Netherlands, and New Zealand.

The Instrument of Surrender was not the later peace treaty. The Treaty of San Francisco, signed in 1951 and effective in 1952, formally ended the state of war between Japan and many Allied countries and established the postwar peace settlement.