Japan's new justice minister Hideki Makihara has said abolishing the death penalty would be "inappropriate" despite the recent acquittal of the world's longest-serving death row prisoner.

Japan and the United States are the only two G7 countries that still use capital punishment, which has strong public support in Japan where scrapping it is rarely discussed.

But the policy -- always carried out by hanging in Japan -- is also criticized for the "cruel" way it is carried out, with prisoners often informed of their impending death in the early morning just a few hours before it happens.

"It would be inappropriate to abolish" the death penalty as "heinous crimes continue to occur", Makihara told reporters on Wednesday after being nominated by Prime Minister Shigeru Ishiba the previous day.

He pledged to be "cautious and extremely sincere" when making the decision to sentence someone to death, according to Nippon Television's online media.

Last week, 88-year-old Iwao Hakamada was found innocent of a quadruple murder he had spent 46 years on death row for.

A Japanese regional court ruled that investigators had tampered with the evidence and said Hakamada had been subject to "inhumane interrogations meant to force a statement".

Hakamada is the fifth death row inmate granted a retrial in Japan's post-war history. All four previous cases also resulted in exonerations.

The country's last execution took place in July 2022, of a man who killed seven in a truck-ramming and stabbing rampage in Tokyo's popular Akihabara electronics district in 2008.