An Asian black bear was seen climbing into a small vehicle at the Gunma Safari Park, northwest of Tokyo, and attacking park employee Kiyomi Saito inside the car, a local police spokesman said.
Saito, 46, suffered injuries to the left side of her chest and stomach and was rushed to hospital where she was later confirmed dead, the spokesman said.
"The details are not yet known, including how the bear got inside the car," he told AFP, adding the animal was a five-year-old male and weighing 160 kilogrammes.
A series of wild bear attacks terrified Japan earlier this year, with four people being killed in the northern part of the country in separate incidents in the wild in May and June.
In 2012, an unknown number of bears escaped from snow-covered Hachimantai bear park in northern Akita prefecture, which had kept 38 animals, most of them brown bears.
Two female workers at the facility were later found dead.