The women, who are in their 20s, were lured to work at the restaurant in central Honshu island November with promise of high wages by a Japanese owner who arranged visas and airfares for the them, the Cambodian foreign ministry said in a statement
"But (he) threatened and forced the victims to have sex with guests at the restaurant and did not pay them salaries," the statement said.
Japanese authorities in Gunma prefecture, west of Tokyo, were then alerted.
Six of the women are now staying at the Cambodian embassy in Tokyo awaiting repatriation tomorrow while the seventh victim was sent home late last month for health reasons.
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Cambodian officials did not say if the Japanese restaurant owner was arrested or faced any charges.
Japan has long been a destination for women from Southeast Asia seeking higher wages who often find themselves forced into sex work or indentured labour.
Washington's annual report on people trafficking says Japan remains a "destination, source and transit" country for human trafficking despite a recent increase in prosecutions.
"Traffickers strictly control the movement of victims using debt bondage, threats of violence or deportation, blackmail, passport retention, and other coercive psychological methods," the State Department's 2016 "Trafficking in Persons" report says.