What was the official title of the document read by Hirohito in his surrender broadcast?

Hirohito read the Imperial Rescript on the Termination of the War in his surrender broadcast.

The rescript was the formal imperial statement announcing Japan’s decision to accept the Allied terms. Hirohito recorded it at the Imperial Palace before the broadcast reached the Japanese public at noon on August 15, 1945.

Its language was indirect and highly formal. Rather than plainly saying that Japan had surrendered, the emperor said he had ordered the government to accept the provisions of the joint declaration, referring to the Potsdam Declaration. The speech also mentioned the “new and most cruel bomb” and the danger of continuing the conflict.

The rescript should not be confused with the Japanese Instrument of Surrender. The rescript announced the decision domestically; the instrument was the international document signed aboard USS Missouri on September 2.