Over the last decade, juvenile crime has become a serious social problem in Japan. The Juvenile Law was revised in 2001 to impose harsher punishment on juvenile offenders. This revision makes it possible to impose criminal punishment on 14- and 15-year-old criminal offenders, while those offenders aged 16-19 have always faced criminal punishment, both before and after the revision. Using this revision as a natural experiment, this study conducts a difference-in-differences estimation to examine the effect of punishment on juvenile crime. The analysis provides evidence that punishment can deter juvenile crime. In addition, this research examines the criminal behaviour of 13-year-olds, who face no change in punishment, but who soon will in the near future. The results suggest that the revision also had a negative impact on the criminal behaviour of these younger offenders.