Prince Hisahito was born last Wednesday
Japan got a first glimpse of its new heir to the throne on Friday as he left hospital in the arms of his mother, Princess Kiko.
Prince Hisahito, who was born last Wednesday, is third in line to the Chrysanthemum Throne, behind Crown Prince Naruhito and his own father.
His birth was widely celebrated, as it headed off a succession crisis.
Only men are allowed to be monarchs in Japan, and Hisahito is the first new heir for four decades.
Princess Kiko, the wife of the emperor's second son Prince Akishino, walked out of the hospital with her baby son in her arms, his forehead just visible above the blankets he was swaddled in.
"I am very grateful to the people, friends and family who prayed for the baby's safe delivery," Princess Kiko said, according to a statement released later by the Imperial Household Agency.
"I am overjoyed by the birth and happy that today we are able to return home," she said.
For the waiting media and hundreds of proud Japanese, it was their first glimpse of the new prince.
Hisahito, whose name means serene and virtuous, slept as the smiling princess posed briefly for photographs with her husband.
Then the family was taken by car through streets packed with well-wishers, some shouting "Banzai", or long life.
The baby's birth has averted a succession crisis in Japan. Emperor Akihito's eldest son, Crown Prince Naruhito, has just one daughter, and until Hisahito's birth, Prince Akishino and his wife had only two girls.
Current Japanese law forbids women from ascending to the throne, and in recent years there have been calls for constitutional reform to change this requirement, to ensure the survival of the monarchy.
The proposal was backed by Prime Minister Junichiro Koizumi, who argued that it would make the succession process more stable.
But many Japanese conservatives were against the move, saying such a change would end centuries of tradition.
The debate was shelved when news of Princess Kiko's pregnancy was announced, but recent polls show that the Japanese public still backs the idea of a female monarch.