Most of the technical high schools in Korea use the same textbooks as general high schools although their goal and textbooks are different from each other. As a result, those students’ participation in class and interest in the English subject are very low. To resolve this problem, this study aims to apply the task-based language teaching (TBLT) to the technical high school classroom and verify the effects of TBLT on students’ affective domains. The participants were 57 first graders in a technical high school. They took part in 50-minute TBLT class for five weeks. Instructional materials were developed for the instruction with practical English expressions focused and participants’ English proficiency levels customized. A student survey questionnaire to measure changes in affective domains (interest, confidence, anxiety, and learning motivation) was administered before and after TBLT classes. The major findings in this study are that the three affective domains such as interest, confidence, and anxiety showed significant improvement; that is, students’ confidence and interest levels increased and anxiety decreased due to the TBLT class. However, the motivation level was not significantly improved after the instruction. It’s imperative for teachers to empower students to participate in their learning process through student-centered class activities and tasks.