The PlayStation Portable (PSP) will soon be opened up to a new and potentially lucrative market - porn.

At least eight pornographic videos will go on sale in Japan exclusively for the PSP, the console Sony is billing as the multimedia Walkman of the 21st century that plays both games and videos.

A Tokyo-based sex-video maker declared on its website that on July 8 it will release the world's first adult UMDs, optical discs that play on a PSP. The five titles carry price tags from 2,800 yen or 3,800 yen (25 or 35 dollars).

Another Tokyo company will launch three titles on July 16.

For its part, Sony said it had no power to stop the release of the PSP porn videos.

"It is difficult for us to impose restrictions," said Sony Computer Entertainment spokesman Koichiro Katsurayama.

He said Sony had shared the specifications for UMDs which do not need approval by the company, unlike PSP game titles which are all licensed.

It is also up to the porn video makers whether they will impose regional restrictions, such as blocking users from playing videos released in Japan on PSPs bought abroad.

The Sony spokesman said the PSP had a locking function that would let worried parents prevent their children from seeing adult videos on the game machine.

He dismissed any idea that Sony saw porn as a commercial boost for the PSP, much in the way that adult titles helped spread videocassette players in the 1970s and 1980s.

"We have no intention of spreading (the PSP) by relying on such titles," he said.

Sony released the PSP in Japan in December and in North America in March in hopes of cracking into Nintendo's dominance of the handheld game-machine market.

It had shipped a combined 2.97 million PSPs by the end of March in Japan and North America. The PSP has yet to be released elsewhere in the world.

From DVD Recordable