Japanese pop star Noriko Sakai was Monday handed a suspended jail term of 18 months for illegal drug use as thousands gathered in a bid to witness the court's decision.

The Tokyo District Court suspended the jail term for Sakai, 38, for three years, after which it will be dropped if she stays crime-free.

She had pleaded guilty to possessing and using unidentified illegal stimulants, and prosecutors had demanded 18 months in prison.

More than 3,000 people lined up for just 21 visitors' seats in the court, including loyal fans who spent the night in a park.

Sakai is a former teenage pop idol turned actress, known in the 1990s for her innocent girl-next-door image and later for her perfect mum persona.

She is also popular in China, Taiwan and South Korea.