Diplomatic records declassified on Thursday indicate that the Foreign Ministry concluded in 1971 that no passport would be needed for the Emperor should he decide to go abroad.
Before Emperor Hirohito's departure on what was his first ever overseas trip that year, the ministry agonized over whether he would require a passport to enter Europe.
Since a passport contains a foreign minister's request to allow the holder to travel without trouble, a ministry document, dated May 10, 1971, said, "It would be inappropriate to issue such a passport for the Emperor or Empress."
The document also said it would be highly inappropriate for the Emperor — who the Constitution states is the symbol of the state and plays a purely ceremonial rather than sovereign role — to undergo immigration or visa procedures using a passport as an ordinary citizen.
Even now, neither the Emperor nor Empress is required to hold a passport for overseas trips. But diplomatic passports are issued for other members of the Imperial family, including the Crown Prince and Princess.
According to the official website of the British monarchy, the Queen does not hold a passport as a British passport is issued in the name of Her Majesty.