Prior evidence suggests that subjective well-being (SWB) remains relatively stable across adulthood. However, longitudinal evidence is sparse except in Western societies such as North America and Western Europe. We examined age-related changes in SWB (life satisfaction, positive affect, and negative affect) among middle-aged and older Japanese. We applied multilevel growth models to 14-year seven-wave longitudinal data of a dynamic cohort study. A total of 3,890 participants aged 40-81 at first assessment were included in the analysis. The longitudinal results demonstrated differential trajectories of SWB. Life satisfaction exhibited an accelerated increase in middle age but decreased and leveled off in old age. Positive affect increased in midlife and declined in late life. Negative affect remained stable in middle age but increased in old age. Demographics, health, and methodological correlates did not fully account for age-related changes in SWB. Of note, increases in negative affect in old age remained evident even after controlling for the correlates. In conclusion, life satisfaction was stable across adulthood, which was not the case with positive and negative affect. We discussed the possible mechanisms in these observed trajectories of SWB, in particular, negative affect in late life.