This study aims to explore the relationship between the preparedness, self-efficacy, career motivation, and job satisfaction of Korean teachers with the 2018 data of TALIS (Teaching and Learning International Survey). For this purpose, 1266 Korean middle school teachers were selected, and an analysis of mediating effects was executed by utilizing structural equation modeling and phantom variables. The results are as follows: teacher preparedness had a significant and positive effect on teacher self-efficacy and career motivation. However, it failed to show a significant effect on teacher job satisfaction, which was instead significantly and positively affected by teacher self-efficacy and career motivation. In addition, based on the analysis of the estimate of mediating effects, it was discovered that teacher career motivation had a greater positive effect than that teacher self-efficacy on teacher job satisfaction. Taking these results into consideration, this study accordingly makes suggestions concerning the improvement of sustainable teacher job satisfaction, self-efficacy and career motivation inside teacher education courses. Furthermore, this study will propose measures such as further valuing the Teaching Personality and Aptitude Test and strengthening in-depth interviews in student teacher selection, extending teaching experiences through simulated instruction and peer supervision as well as providing well-organized teaching professional counseling opportunities for student teachers.