A telephone survey conducted by the Japan Federation of Bar Associations has prompted 125 complaints of human rights violations at correctional facilities across the country.
The survey was conducted at the beginning of March by 36 bar associations nationwide and a group of bar associations in the Kinki region, the federation said.
It followed revelations of inmate abuse at Nagoya Prison that resulted in two deaths.
Of the 125 complaints, 73 were submitted by former inmates and centered on human rights violations experienced either by themselves or by other inmates, the federation said.
The remainder were submitted by relatives of former inmates and others.
Fifty-eight complaints involved some form of violence, including the use of leather manacles and a metal baseball bat, while 34 involved inappropriate medical treatment.
The federation plans to submit the results of the survey to a Justice Ministry panel tasked with discussing prison reform measures.
Justice Minister Mayumi Moriyama visited Nagoya Prison in Miyoshi, Aichi Prefecture, on Friday to inspect cells and medical facilities for the first time since the incidents were made public last year.
"I want to deeply apologize to the people in the country," she told a news conference after the visit.
Moriyama said she had told Nagoya Prison executives about the importance of re-establishing public trust.