Bullying cases recognized by schools between April and September more than doubled to 144,054 from about 70,000 for all of the previous school year, according to the education ministry.
The total includes 278 serious cases that could have endangered the lives, or at least the physical safety, of students, the ministry said Thursday.
The figures cover elementary schools through high schools, as well as schools for students with special needs, and showed a sharp increase due to growing awareness of bullying in schools, the ministry said.
By prefecture, Kagoshima recorded the most bullying cases: 1 per 6 students. This was about 160 times greater than in Fukuoka, which had the lowest rate, at 1 case per 1,000 students.
Education ministry officials said the figures could fluctuate significantly depending on school authorities' perception of and approach toward bullying.
The tally was compiled on the basis of reports sent as of Sept. 22 from prefectures across the country.
The ministry ordered them in August to conduct a survey of bullying after a 13-year-old junior high school boy in Otsu, Shiga Prefecture, committed suicide in October 2011 after being repeatedly bullied.
By school, about 88,000 cases of bullying were reported at elementary schools, roughly 43,000 cases at junior high schools, some 13,000 cases at high schools and about 600 cases at special schools for disabled students.