Which document did Japan accept before signing its formal 1945 surrender?

Japan accepted the Potsdam Declaration before signing its formal 1945 surrender. The declaration set out Allied terms for ending the war against Japan.

The United States, the United Kingdom, and China issued it on 26 July 1945 during the Potsdam Conference. It called for the unconditional surrender of Japan's armed forces and warned of “prompt and utter destruction” if Japan refused. The Soviet Union was not yet at war with Japan when the declaration was issued, so Joseph Stalin was not one of its original signatories.

Japan announced acceptance of the declaration in August after the atomic bombings, the Soviet entry into the war against Japan, and intense internal debate. Acceptance was a political decision; the formal legal act came on 2 September through the Japanese Instrument of Surrender. The Potsdam Declaration is therefore not the surrender document itself, although its terms formed the basis of Japan's capitulation.