This study is intended to investigate the effect of regret on subjective well-being and the adaptive coping strategy to regret targeting 158 middle-aged women living in Busan. And there are two contrasting principles with regard to the possibility of modification perceived in regret itself and its regret: a future opportunity principle and a lost opportunity principle; while a future opportunity principle argues that in relation to regret experiences the more possibility of regret people perceive the more regret they feel, a lost opportunity principle argues that in relation to regret experiences the less possibility of regret people perceive the more regret they feel. This study is aimed to identify which theory among the two can describe regret better by investigating the effect that the possibility of modification perceived has on regret emotion and happiness. First, results showed that the more emotion related to regret they felt the less happy they were, while the areas in life where the middle-aged women felt regret most frequently were ‘love and selection of spouse’, ‘lack of education’, and ‘self’. Second, it was indicated that the more they used the regret rumination among the coping strategies to regret, the more emotion related to regret they felt and the less happy they were while the more they used a strategy seeking for an alternative object the less happy they were. Third, It was revealed that the less possibility of modification perceived in regret experiences there was, the more emotion in relation to regret they felt and the less happy they were, which supporting the lost opportunity principle. Finally, the result of path analysis showed that the possibility of modification perceived and the regret rumination had an effect on happiness both directly and indirectly by the medium of regret-related emotion. A strategy seeking for an alternative object only had a direct effect on happiness.