Japanese screenwriter Sakamoto Yuji, who has won the Best Screenplay award at the Cannes Film Festival for "Monster", says he feels like he is still in a dream.

Sakamoto appeared at a news conference on Monday alongside the director of the film, Koreeda Hirokazu, who arrived in Japan from France earlier in the day.

The story centers around an incident stemming from a quarrel between elementary school students. The incident is recounted from the viewpoints of the parents, teachers and others, posing the question of what the "monster" is.

Sakamoto spoke at the news conference after receiving his trophy from Koreeda, who attended the awards ceremony on Saturday.

Sakamoto said he was in bed when he heard the news, and that it has yet to sink in. He said he feels responsibility rather than joy. He said the weight of the prize is a burden he has to carry.

Sakamoto said he wrote the screenplay thinking about those who live a lonely life somewhere in the world and believing that they will come to understand the heart of the story.

Asked whether he wants to work with director Koreeda again, Sakamoto said he would be happy to, if he is offered the chance. He said he respects Koreeda both as a director and a screenwriter.

Koreeda said he is always happy when he receives compliments on his cast and staff, though he is doubtful whenever he himself is praised.

The film opens in theaters across Japan on June 2.