ONOMICHI, Hiroshima Pref. — Handrails run down the middle of the hallway to help prisoners make their way from one end to the other. Adult diapers are neatly stacked in a corner. When an inmate chokes on his rice and coughs, a supervisor rushes over to rub his back.

Welcome to the world of old-age prisons. The rise in elderly inmates is even sharper than the aging of Japan in general.

The number of prisoners aged 60 or older has doubled during the past decade to more than 10,000. That outpaces a 30 percent increase in the general population for that age group. The elderly now represent 16 percent of all inmates.