The purpose of this study is to verify the structural relationship between job crafting and job enthusiasm, informal learning, social support, and positive psychological capital, and to investigate the effect of informal learning, social support, and positive psychological capital on job crafting through job enthusiasm. A survey was conducted on 451 safety workers at large domestic companies, and the collected data were analyzed for model suitability, influence relations between variables, and mediating effects with AMOS 23.0 using SPSS 23.0. Through research, we found five important results. First, the structural model of job crafting, job enthusiasm, informal learning, social support, and positive psychological capital properly explained the empirical data. Second, social support and positive psychological capital had a positive effect on job enthusiasm, but informal learning did not significantly affect job enthusiasm. Third, informal learning and positive psychological capital had a positive effect on job crafting, while social support did not significantly affect job crafting. Fourth, job enthusiasm had a positive effect on job crafting. Finally, job enthusiasm was found to mediate the relationship between social support and positive psychological capital and job crafting. These suggest that continuous environmental efforts and systematic management measures are needed to promote job crafting of safety workers so that informal learning, social support, positive psychological capital, and job enthusiasm can be expressed. Therefore, the necessity of developing various sub-factors of informal learning that can promote job crafting of safety workers was suggested as a follow-up study.