This number seems insignificant to me. If there are 934,230 teachers in Japan (2001 data) and 24% of Japanese suffer from mental illnesshttp://www.japantoday.com/category/arts-culture/view/new-documentary-explores-taboo-subject-of-mental-illness-in-japan (2009 documentary) then that would mean 0.53% of teachers have taken leave for mental illness.
options: 1. The numbers are low because reasons for leave-taking are recorded as other illnesses.
2. Administrations adjusting the numbers to deliver a different message.
3. Health issues inappropriately diagnosed.
4.23.5% of teachers are not taking leave for mental illness.
5. Teachers have a very much higher rate of mental health than the general population.