This study focused on the motivational process of the Job Demands-Resources Model (JD-R model), a model that explains work engagement. The first objective of this study was to develop a scale to measure positive emotional experiences of high school teachers. The second objective was to examine factors affecting work engagement. First, we collected items from responses to semi-structured interviews with 10 high school teachers and from previous studies. Next, a questionnaire (the Positive Emotional Experience Scale) consisted of the above-mentioned items was administered to 239 high school teachers. The results of factor analysis yielded three factors: “student growth,” “teacher contribution,” and “workplace collaboration.” Reliability and validity were found at a moderate level for each factor. For the second objective, structural equation modeling was conducted assuming a model in which positive affective experiences and personal resources enhance intrinsic learning motivation for subject instruction through work engagement. The results showed that the model was an acceptable fit. Finally, we discussed ways to support the mental health of high school teachers.