Shoko Asahara was convicted in 2004 and sentenced to hang for masterminding the attack, in which members of the Aum Shinrikyo doomsday cult released deadly sarin gas on trains converging on the city’s government district. Besides the dead, thousands were hospitalized.
Asahara’s lawyers filed an appeal with the Supreme Court after the Tokyo High Court threw out a similar appeal in March, the Kyodo News agency reported.
His lawyers argued that their client suffers from pathological mental stress caused by confinement and was unfit for trial.
The lawyers could not be reached late Monday to confirm the report.
The nearly blind former leader, who once commanded a powerful group with about 40,000 members, mumbled incoherently during his trial, interrupting sessions with bizarre outbursts in English. Last month, a court-appointed psychiatrist said Asahara may have been feigning mental illness.
Asahara has also been convicted of plotting a 1994 gas attack in the central Japanese city of Matsumoto that killed seven people, the kidnapping and murder of an anti-cult lawyer and his family, and other slayings.
About a dozen other Aum Shinrikyo leaders have been sentenced to death, although none has been executed.
Three members wanted in connection with the subway gassing remain at large.
At its height, the cult claimed 10,000 followers in Japan and another 30,000 in Russia. Now named Aleph, the group has about 6,500 members and is under surveillance by Japan’s Public Safety Agency.