Prosecutors demanded a three-year prison term for disgraced pop singer Aska on Thursday as his trial over illegal drug use kicked off at the Tokyo District Court.

The singer, half of the long-running duo Chage and Aska, pleaded guilty to all charges, including breaking the Stimulant Control Law and the Narcotics Control Law.

"I'm terribly sorry for betraying my fans and anyone concerned," said the 56-year-old, whose real name is Shigeaki Miyazaki.