The 72-year-old man convicted last week in the first lay judge trial has filed an appeal, sources said Thursday.
The Tokyo High Court appeal won't involve lay judges.
Katsuyoshi Fujii was sentenced to 15 years by the panel of six citizen and three professional judges in a four-day trial at the Tokyo District Court earlier this month for stabbing and murdering a 66-year-old neighbor in Tokyo in May.
His lawyers sought leniency, claiming the incident occurred accidentally after a quarrel between the defendant and victim, while prosecutors demanded he receive 16 years in prison.
Whether professional judges at the high court will overturn the ruling or reduce Fujii's sentence, in which lay judges had a hand, will be the focus of the appeal.
In November, the Legal Training and Research Institute of the Supreme Court said in a report that a high court should respect a lay judge trial ruling unless the facts and the prison term decided by the district court were "extremely unreasonable."
Recommendations in the report are unbinding but are expected to influence judgments at high courts.
At the district court, the panel of judges rejected Fujii's side of the argument that the victim had engaged in provocative behavior that led him to stab her to death, giving him a sentence just one year shorter than demanded.
Under the lay judge system, six citizens randomly chosen from the voters sit together with three professional judges to decide the facts about a case based on the evidence presented. Should they find the accused guilty, they will also decide the sentence.
The vote is decided on a conditional majority, where at least one professional judge must be included in the majority decision. The lay judges are prohibited from revealing the details of the deliberations, including their vote count.