Sogen Kato was thought to be the oldest man in Tokyo. Welfare officials had tried to meet Mr Kato since early this year. However, family members repeatedly chased them away.
Authorities grew suspicious and sought an investigation by police, who forced their way into the house on Wednesday. They discovered a mummified body lying in his bed.
Jiji Press reported that his relatives said he had confined himself in his room more than 30 years ago and became a living Buddha.
But the family, who will be investigated for fraud, had received 9.5 million yen ($109,000: £70,000) in widower's pension payments via Mr Kato's bank account. The pension fund had long been unable to contact him.
"His family must have known he has been dead all these years and acted as if nothing happened. It's so eerie," a Tokyo metropolitan welfare official reported.
Aside from one family's deception, why are people living so long nowadays? According to latest Office for National Statistics data, there are more than 13,000 centenarians living in the UK, but by 2066 that number is expected to increase to more than 500,000.
The study by King's College London found they were more likely to die of infections such as pneumonia.
Can society go on supporting a progressively aging population?
A catastrophic situation is developing in England with many vulnerable elderly people and disabled people being denied care, campaigners say.
An analysis by Age UK found the proportion of over-65s getting help had fallen by a third since 2005-6. Over 800,000 older people were living without vital assistance. This includes council-funded help in the home with daily tasks such as washing, dressing and eating as well as care home places.
Government and local funding need to focus on keeping people well and living independently for as long as possible. But with fewer people working to support an aging population, that will be difficult. Of course, the ideal solution is for families to take their aging parents into their own homes. However, these days, circumstances have caused relatives to live far away from each other or overseas which makes that scenario impossible. Also, the modern lifestyle doesn't allow a place in a busy working woman's tiny home.
And that raises the question of whether I'm of any use to society. My husband thinks I'm invaluable, but he's in the minority. I'd hoped to show through my writing that practically everybody can make a good decision in difficult times. In the novels Still Rock Water & Tidal Surge, Liliha acts as the little voice whispering inside all of us if only we'd listen. But just as I'm but a grain of sand on one of the many beaches of Earth, so my novels are surrounded by others, rarely exposed by a passing wave of interest.
Now in my 70s, my continued existence is in God's hands. However, I'm the only one who can market my books. It is in your power to make an old woman happy, gain self respect, and to know she's fulfilled her potential. (Although I long for that to happen, my tongue is firmly in my cheek.)