TOKYO (AFP) - A 67-year-old woman was arrested on Wednesday on suspicion of poisoning her husband with cyanide, as it emerged six former partners had already died, in Japan's latest apparent "black widow" case.

Chisako Kakehi has been the beneficiary of a combined 800 million yen (S$8.88 million) over the last two decades, Jiji Press said, the insurance money and other assets she received after the seven men's deaths.

Husband No. 4 Isao Kakehi fell sick suddenly at home and was confirmed dead at a hospital in December last year, less than two months after the couple married. An autopsy found highly toxic cyanide compounds in his blood.

That came after the September death of a 75-year-old boyfriend, who fell suddenly ill after the couple ate together at a restaurant, Jiji said.

Kakehi's dalliance with death began in 1994, when her first husband died at the age of 54.

In 2006, her second husband died of a stroke at the age of 69, while the third marriage ended in 2008 with the death of her 75-year-old partner, Jiji said.

A boyfriend, believed to have been suffering from some form of cancer, died a year later, and in 2012, her then fiance died after collapsing while riding a motorbike.

Traces of cyanide were detected in his body, media reports said.

Kakehi was arrested on Wednesday by police in Kyoto on suspicion of murdering her latest husband. She has denied any involvement in his death.

Questioned by reporters earlier this year, the former bank worker protested her innocence.

"If people suspect murder, I'd find it easier to bite my tongue off and die," she told reporters in March, television footage showed.

In 2012, a woman in her 30s was sentenced to death in another "black widow" case, named for the female spider that eats its mate after coupling.

Kanae Kijima was sentenced to hang for the murders of three men, aged 41, 53 and 80, whom she met through Internet dating sites.

She is in jail awaiting the outcome of an appeal to the Supreme Court.