TOKYO, Sept 6, 2007 (AFP) - Prince Hisahito, the first male heir born to Japan's royal family in four decades, celebrated his first birthday Thursday with public attention glued to his every move.

The baby prince, carried by his mother Princess Kiko, looked surprised in the glare of cameras as he arrived at the imperial palace to greet his grandparents Emperor Akihito and Empress Michiko.

The prince, the first boy born to the family since his father Prince Akishino, is third in line to the Chrysanthemum Throne, the world's oldest monarchy.

His birth all but ended a growing debate in Japan over whether to allow female progenitor.

Newspapers published front-page pictures of the prince smiling broadly as he stood on a table in pale blue rompers. The Imperial Household Agency said he weighs 9,285 grams (20.4 pounds) and is 75 centimetres (30 inches) tall.

The agency released video footage of the family reading with the prince, who resembles his father, the emperor's second son. The boy has two teenage sisters.

"His Highness Prince Hisahito is walking with support and crawling on stairs and his activity has grown vigorous particularly in the past month," the agency said in a statement, adding that he claps his hands to music and likes to play the piano, drums and harp.

"He likes picture books and turns the pages himself. When he comes to the end of a book, he then looks at the front and back covers," it said.

Hisahito is third in line to the throne after his uncle Crown Prince Naruhito and his father Akishino.

Naruhito is married to Princess Masako, a former career diplomat who has made few public appearances since 2003 due to stress as she tries to cope with palace life.

The couple's only child is five-year-old Princess Aiko. Until her sister-in-law's pregnancy, Masako was under intense pressure to produce a male heir.

The emperor enjoys wide respect among the Japanese people but has no political role under the post-World War II constitution.