Yuuya Yagira speaking to director Hirokazu Koreeda by phone

Yagira, 14, took the best actor prize for his role in Nobody Knows, about children abandoned by their mother.

"I was previously unable to decide between a soccer player or an actor, but now I am convinced I should work hard as an actor," he said.

Yagira missed Saturday's ceremony because he returned home to sit exams.

He landed the part in his first audition, and said he acted in the movie just the way he was told by director Hirokazu Koreeda.

"I am very happy although I wondered if it is OK to be given this big award," he said.

Real-life story

Speaking to journalists in Tokyo, he said he had received messages on his mobile phone from friends congratulating him on his success.

Yagira was picked by a jury led by Pulp Fiction director Quentin Tarantino. The main Palme d'Or prize went to Michael Moore's documentary Fahrenheit 9/11.

He plays the oldest of four children in the film, which is based on a real-life story.

"If adults watch the movie, I want to tell them, 'Don't abandon kids, don't treat them like a toy," he said.

Tokyo film critic Reiko Kubo said Yagira deserved his award.

"When I saw the movie, I thought the director had made a very good choice in casting - but his age and inexperience made me doubt if he could win the best actor award," she said.