The tasks of probation officer are twofold: case investigation and offender supervision. Case investigation includes preparation of the presentence report(PSR), which provides basic information on the sentencing and the eligibility for probation. The work of case investigation has been developed closely associating with offender supervision. The presentence report helps in deciding for or against probation and serves as the basis for a plan of probation supervision and treatment. Therefore, the appropriate use of presentence report will have a strong influence on the possibility of successful probation. Although the importance and the need of presentence report have increased, the rate of using presentence report by the court is decreasing. To overcome this trend, the structured and practical measures are required as follows. First, relating to the current controversial ‘sentencing investigation system’, it is reasonable that probation officers are charge of the investigation. Probation officers are professional investigators through the experiences of writing approximately 50,000 presentence reports over the past 25 years, and they can make a fair and objective report because they are independent from the parties concerned to the sentencing. Moreover, in most countries, probation officers are responsible for the presentence investigation. Second, it is urgent to secure the personnel of investigation and establish additional investigation divisions. Third, it is required to operate ‘the investigator certificate system’ separating into ‘advanced investigator’ and ‘ general investigator’ to enhance the specialization. The investigation should be mainly conducted by investigators who have a certificate of investigator to boost the purpose and public confidence of the certificate system.