No students were hurt in the attack in Neyagawa City outside Osaka, said Isoo Noda, spokesman for the Neyagawa City police, but the stabbings came as the latest in a series of rampages in Japan involving knives and children.
Police arrested a teenage boy who was a former student at the school in the faculty room, saying he used an 8-inch kitchen knife to stab two teachers and a school nutritionist. They found him smoking a cigarette in the room as frightened teachers looked on from afar, Noda said.
A 52-year-old male teacher was declared dead after the assault while a 57-year-old female teacher was seriously injured with knife wounds in her stomach, police said. The nutritionist, 45, was also being treated for injuries.
"I couldn't believe it," said the principal, Hirokazu Sakane, speaking at a news conference televised nationally in a country on edge from the repeated stabbing attacks. "It is unforgivable. It is especially mortifying that a staff member lost his life."
The attack triggered panic at the school, which has about 600 students and 32 teachers. National broadcaster NHK showed aerial footage of students running frantically out of the building and gathering in the playground.
While violent crime is still relatively rare in Japan, juvenile delinquency is on the rise, according to police statistics.
In 2002, the government lowered the age for which juveniles can be prosecuted as criminals to 14 from 16, partly in response to a 1997 incident when a 14-year-old beheaded an 11-year-old neighbor.
Also, in 2001 a Japanese man with a history of mental illness barged through several classrooms in Osaka in western Japan and stabbed dozens of children and teachers. Eight children died and 13 others, including two teachers, were injured. Mamoru Takuma was found guilty of the murders and executed last September.
In June, an 11-year-old girl led a 12-year-old classmate into an empty classroom in southwest Japan and slit her neck and arms, leaving the girl to bleed to death. The attacker told police the other girl had been posting unfriendly notes on the attacker's home page on the Internet.
Earlier this month, a man armed with a kitchen knife went on a stabbing spree in the children's department of a supermarket in central Japan, killing an 11-month-old boy and injuring a 3-year-old girl and an adult woman, police said.
The attacks had led to calls for greater security at schools, and many have since put up gates and installed guards at entrances to keep out strangers.
It was not clear how the attacker entered the school on Monday. The school did not post security guards at its entrance while gates to the campus would have been open at the hour of the attack since it was time for younger students to go home for the day, said Chiharu Tsukuda, a spokeswoman for the Neyagawa Board of Education.
The teenager, whose name was not released because he is a minor, graduated from the school, said Hirokazu Kashiyama, a local school board official.
Kashiyama did not have information on the boy's attendance record, but Japanese media reported he was a poor student: he had started regularly skipping class from the time he was in elementary school.