This study examined whether the avoidant response style to positive affect moderates the effects of nostalgia on self-continuity, mental well-being, and positive affect in early adulthood. 133 adults aged 18 to 29 nationwide were randomly assigned to an experimental group, a comparison group, and a control group, and received treatment or waited without treatment. All participants responded to pre, post, and follow-up questionnaires. The results of this study are summarized as follows. First, nostalgia intervention had a positive effect on self-continuity, but did not significantly affect mental well-being and positive affect. Second, the effects of nostalgia intervention on self-continuity were maintained two weeks later. Third, the avoidant response style to positive affect moderated the relationship between nostalgia intervention and mental well-being, but did not moderate the effects on self-continuity and positive affect. This study confirmed that nostalgia intervention promotes self-continuity and contributes to mental well-being interacting with emotion regulation skills in early adults.