Prosecutors said they wanted an 18-month jail term for Ms Sakai
More than 6,000 people have queued for the 20 seats in a Tokyo courtroom's public gallery to see a famous Japanese singer and actress go on trial.
Noriko Sakai, 38, has pleaded guilty to using and possessing illegal drugs.
The case has gripped Japan since August when her husband was arrested and she went on the run for a week before turning herself in to the police.
Prosecutors say she took amphetamines in July and that police found a small amount of the drug in her Tokyo home.
In Monday's hearing, she pleaded guilty to possessing 0.008 of a gram of a stimulant drug and of using drugs too.
Police say that after she went on the run, more drugs were found in her apartment.
Prosecutors said they wanted an 18-month prison term for Ms Sakai.
She told the court that using drugs had been her own decision, Kyodo News agency reported.
"It was a very thoughtless act," she added.
She said she wants to divorce her husband and make a fresh start in nursing care for the elderly.
"I must correct myself. I feel miserable," she said. Her husband is being tried separately on similar charges.
Ms Sakai rose to fame in 1987 after releasing a single, Otoko no Ko ni Naritai, a few days before her 16th birthday.
Known as Nori-P during her early career, she began to use her real name after turning to acting in the 1990s.
One of her most acclaimed roles came in the TV melodrama Hitotsu Yane no Shita.