The government is being asked to pressure China over an arrest it made last year in connection with the Falun Gong spiritual movement.
Atsushi Kaneko is worried that the Chinese government may not release his Chinese wife, Yoko Kaneko, when her 18-month detention expires Sunday.
Yoko was arrested May 24, 2002, for violating a Chinese law banning "evil cults" while she and some friends were distributing Falun Gong leaflets in Beijing.
"Past cases show that the (detention) period may be mercilessly extended due to unfair reasons," Atsushi said in a petition he submitted Monday to Foreign Minister Yoriko Kawaguchi.
"I hope she will be released for certain on Nov. 23," he told reporters afterward.
Falun Gong followers are often subjected to torture and other harassment in China when they refuse to leave the organization, according to Amnesty International Japan.
During a news conference Friday, Kawaguchi said Yoko Kaneko would not ordinarily receive protective custody because she is not a Japanese national. "But the ministry has approached the Chinese government about her case on various occasions since she is married to a Japanese and had been living in Japan," she said.