In modern society, the filtering of illegal or harmful content on the Internet is necessary for the healthy development of young people. However, the mental damage that Internet filtering workers may suffer has been overlooked. We examined occupational stress and related factors among Internet filtering workers in Japan. Workers (N＝160) in a company providing a web-content filtering service completed a questionnaire. The percentage of all respondents with high-risk Impact of Event Scale Revised (IES-R) scores was 10.4％ and with high-risk General Health Questionnaire (GHQ-12) scores was 47.0％. These results indicated that rates of mental damage among Internet filtering workers were as high as those of firefighters and journalists. IES-R and GHQ-12 scores were used as the dependent variables in the quantification method (Type 1). The results showed that these scores related to stress responses in the aftermath of witnessing traumatic illegal or harmful content, emotional empathy, and so on.