Osaka residents Yasutaka Kakimoto, 55, and his wife Yukari, 53, admitted to locking their daughter Airi in a small room from the age of around 16 or 17, Kyodo News said.
An autopsy showed Airi had frozen to death and was extremely malnourished, weighing about 19 kilogrammes (42 pounds).
The parents told police they confined their daughter because she was mentally ill and acted violently, national broadcaster NHK said, adding that the room had an intercom that the family used to communicate.
They reportedly fed their daughter about once a day.
After reporting her death to police, the couple were initially charged with illegally disposing of a body but police were also considering other charges including confinement, Kyodo said.
Osaka police did not immediately respond to requests for comment Wednesday evening.
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