As serious offenses committed by adults decreased in the 1970's, Japanese police had more time to regulate minor offenses. Therefore, the increase in juvenile offenders was caused by increases in minor offenses or delinquent acts detected by the police. Under Japanese law, all juvenile cases are referred to the family courts. Juvenile traffic offenders overburdened these courts in the 1960's, but now are diverted to the police. Even with increases in juveniles caught by the police, the number of cases referred to the family courts was less in 1982 than in the 1960's. Probation officers investigate all juveniles referred to family courts and recommend protective education measures only when a youth has committed a serious offense or lacks protective surroundings. Most juvenile nontraffic offenders in the family courts are dismissed without hearing, and this proportion rose from 55.7 percent in 1965 to 70.5 percent in 1981. As Japanese society stabilized during the two decades after World War II, serious juvenile offenses decreased and training schools became less crowded. In the 1970's their resources improved, and they began to have good effects on inmates. Some schools began to successfully treat for short periods traffic offenders and juveniles charged with less serious offenses. Tentative probation allows a probation officer to supervise juveniles for a time before writing a report to the court, and it can be custodial, with the probationer living with a volunteer; or it may be noncustodial. Custodial tentative probation has declined recently because of the development of effective short-term treatment in training schools and problems inherent in matching juveniles with suitable volunteers. Footnotes, graphs, and tables are supplied.