In a room called "the care factory" in Fuchu Prison in western Tokyo, eight elderly inmates sat at low tables making small paper bags last month. According to a prison officer, the prison went to several businesses to ask for ideas on jobs that can be done by elderly people whose physical strength is fading.

The Japanese-style room with a space of about 24 tatami mats is equipped with a small kitchen and beds. The eight shaven-headed inmates eat and sleep there together.

"It's a last resort," a prison officer said. "But elderly people move slowly and can't keep up with group activities."

Other prisons across the nation are grappling with how to handle the rapidly increasing population of elderly inmates.

According to the Justice Ministry, the total number of inmates as of the end of 2011 was 61,102, down nearly 10,000 from the peak at the end of 2006.

Although this was in line with the decrease in criminal offenses, the number of inmates aged 70 or older continues to rise and reached 2,524 at the end of last year--2.9 times the figure at the end of 2001.