Suicide is a major public health issue. In Japan, local governments are responsible for suicide prevention, and local government officers are therefore expected to act as gatekeepers for suicide prevention. In this study, through a questionnaire survey, the authors examined the current knowledge and attitudes concerning suicide prevention among local government officers and healthcare and welfare professionals, and the effects of providing suicide prevention education on their knowledge of and attitudes toward suicide and its prevention. One hundred eighty-three local government officers and 432 healthcare/welfare professionals completed the survey before and after a single education session. Before the session, the local government officers and healthcare/welfare professionals showed mainly positive attitudes toward suicide prevention efforts, with little difference between the two groups. After the training, knowledge and attitudes were further improved for most questionnaire items. Respondents with one or more experiences of suicide prevention training showed significantly more knowledge and positive attitudes before the training than those with no such experience. Moreover, knowledge of depression and having a sympathetic attitude were found to be especially associated with the overall attitude that “suicide can be prevented”. Training in suicide prevention was shown to be effective in promoting appropriate knowledge and attitudes among local government officers and healthcare/welfare professionals who are gatekeepers for preventing suicide. Our findings confirm the importance of suicide prevention education, and will contribute to creating a standard educational program on suicide prevention in Japan.