Objective: The choice of emotion regulation (ER) strategies depends on contextual characteristics, and the flexible choice of ER strategies based on context is essential for psychological health, including depression. Focusing on reappraisal, this study examined how perceived reappraisal affordances (the inherent potential of a situation for semantic reappraisal)—a reappraisal-related situational factor—are linked to the success of reappraisal use via reappraisal choice and investigated the role of depression in this mediation. Methods: Eighty participants (40 individuals with major depressive disorder [MDD] and 40 non-depressed controls) read eight vignettes describing negative-emotion-evoking situations and reported reappraisal affordance, the likelihood of choosing reappraisal, and negative emotional responses for each vignette. Then, they were asked to implement reappraisal for each situation, followed by reporting their negative emotional responses again. Results: Reappraisal affordance predicted greater reductions in negative emotions following reappraisal use (i.e., greater success) via an increased choice of the strategy. Group moderated the affordance-choice relationship, with a significant positive relationship observed only in the MDD group, while the relationship was not significant in the controls. Conclusion These results support the idea that considering contextual factors is crucial in understanding ER; however, adjusting ER choice based on situational factors may not always reflect flexible ER, as indicated by the significant affordance-choice link only in the MDD group.