Boys of the same age average just over four hours mobile phone use a day, the survey by information security firm Digital Arts, published Monday, said.
Teenagers tend to use their phones for social media, such as Line, a Japanese messaging and networking app, as well as smartphone games, making movies and other sharing apps like Instagram.
The poll comes amid growing concern over youngsters getting addicted to their portable technology, with Chinese research showing heavy phone use provokes the same kind of neurological changes as alcohol or cocaine dependency.
A total 96 percent of Japanese high schoolers have a mobile phone, against 60 percent of junior high school students, Digital Arts said. Almost four in every ten children in the upper years of elementary school — from the age of 10 — use a mobile.
The survey, which was carried out online, quizzed 618 children from schools across Japan.