The city of Hirakata, Osaka Prefecture, mistakenly accepted a marriage registration form from a 17-year-old boy, despite it being illegal under civil law for males under 18 to wed, sources said Thursday.
His wife, also 17, was eligible to marry under the law, which allows females 16 and older to wed.
Marriage registration cannot be annulled unless it is withdrawn by the couple or their relatives, meaning the marriage is legally valid, they said.
"It was a simple, careless mistake," said Mitsunori Amiya, chief of the city's civil service section. "We sincerely apologize for the inconvenience we imposed on those concerned."
According to the city, the marriage registration was submitted by the wife and the husband's mother June 12. A city official who accepted the document failed to notice that the husband is two months short of his 18th birthday.
A photocopy of the marriage registration document was delivered the following day to the municipal government of the wife's hometown, which pointed out to the Hirakata city office that the marriage may not be legitimate because of the husband's age.
The Hirakata city office said it then contacted the couple, who asked the city to register them as married because their marriage is supported by both of their families.
The document was complete with seals of approval by the parents of both wife and husband, which is required in a marriage between minors.