"I was telling people over dinner, and I could only get half way through the story and I would start crying," the Hollywood star told a news conference after the film was screened out of competition at the Rome Film Festival.
The true story of a friendship between the dog Hachiko and his owner is a legend among Japanese, a pet-loving nation that honors self-sacrificing loyalty.
Hachiko used to wait every day at Shibuya train station for its owner, a professor at the University of Tokyo - even for a decade after the professor died. People were so moved they built a statue of Hachiko at the station - now a popular rendezvous spot.
The story of Hachiko, who himself died in 1935, was made into a 1987 Japanese movie.
The new version, directed by Lasse Hallstrom, moves the tale to a station in modern Rhode Island.
"I cried like a baby" when reading the script, Gere said. "I wasn't sure if it was just a very sensitive reaction I had that day, so I read it again a few days later and had the same reaction.
"This is a love story," said Gere, who plays the professor. "It has nothing to do with gender or species."
The canines that play Hachiko in the movie belong to the Japanese breed of Akita dogs - known for being close to wild dogs and very difficult to train.
"We could not train the dogs to do things, but we had to create an environment trustful for them," Gere said.
The movie had its U.S. premiere in June at the Seattle International Film Festival, and opened in Japan in August.
Other movies screening out of competition at the Rome festival include "Julie & Julia," starring Meryl Streep and Amy Adams, and Joel and Ethan Coen's film "A Serious Man."
The fourth edition of the festival, which is becoming part of the international circuit of movie festivals, runs through Oct. 22.