The purpose of this study was to conduct process evaluation of a web-based stress management program, which was designed to improve psychological well-being as a positive psychological function of humans. A total of 168 employees participated in the intervention. The pre-test was conducted at the time of registration and the post-test upon the completion of the program. Participants are requested to evaluate program sessions by answering four questions (informative, enjoyment, intention to act, self-efficacy belief). Participant evaluations of the sessions were also used as the mediating variable that influences program outcomes. For analysis, we built a model based on the program impact theory and conducted path analysis. Result revealed the majority of participants evaluated the program affirmatively in all sessions and the participant evaluations about the sessions directly predicted changes in psychological well-being (β=0.29, p<0.01), and changes in the psychological well-being predicted changes in the scores of CES-D (Center for Epidemiologic Studies Depression Rating Scale), which represent the level of depression (β=0.50, p<0.001). In conclusion, the program can be effective if the participants feel enjoyment, and increase their intention and self-efficacy belief to cope with stress.