A survey shows that more than 90 percent of public junior high schools in Yokohama City, near Tokyo, allotted only 15 minutes for student lunches in the last fiscal year.
The city's board of education surveyed all 148 public junior high schools in response to concerns raised by parents.
It found that most schools set lunch preparation time at only five minutes in the school year that ended in March.
One-hundred and thirty-five schools, or over 90 percent, had 15-minute lunchtimes. The remaining 13 schools allotted 20 minutes.
Board officials say such time allocation has been practiced for years and that teachers cite difficulties in setting aside enough time for lunch.
Japan's education ministry gives no specific targets for lunchtime in its guidelines. But it calls for creating an environment where students can have pleasant meals in a comfortable atmosphere.
The board officials are calling for longer lunchtimes from the viewpoint of dietary education and students' development.
Board member Noriaki Kimura said children grow rapidly and that their junior high school days are especially important for acquiring desirable eating habits. He said the board will continue urging schools to ensure enough time for lunch.