In this paper, the problems of Sentencing Investigation System are examined, and and the improvements of Sentencing Investigation System are suggested. The main contents are briefly summarized as follows. First, when we discuss the problems of the sentencing investigation system and the ways to improve it, it is necessary to consider that the number of the probation officer is not enough for pre-prosecution investigation, pre-sentencing investigation, probation work and sentencing investigation. And the probation officer`s pre-prosecution investigation, pre-sentencing investigation and probation work need professionalism, but sentencing investigation by investigator needs the justice of the investigation into objective facts. So if the probation officer and investigator`s work are divided up efficiently for professionalism and specialty, the repetitious work done by different departments and the waste of human resources will be avoided. We will need to discuss the sentencing investigation system on the premise those things. Second, it is necessary to revise the criminal procedure act and the probation law for dividing up the probation officer and investigator`s job efficiently. In other words we need to make legal ground about the contents, means and procedures of the investigator`s sentencing investigation system in the criminal procedure act. It is necessary to divide up the work by revising the probation law as follows; the probation officer should carry on the pre-prosecution investigation, the pre-sentencing investigation and the probation work. And the investigator should carry on the sentencing investigation. Third, because the current number of investigators is not enough for the demand of the sentencing investigation according to the implementation of the sentencing guidelines, it is necessary to recruit enough manpower. Also it is important to hire enough probation officers continuously through the appropriate demand survey because there are probation officer shortages for pre-prosecution investigation, pre-sentencing investigation and probation works. In conclusion, the investigators should be let carry out the sentencing investigation by revising the criminal procedure law for applying the sentencing guidelines rightly. Also the probation officers should be able to execute the pre-sentencing investigation, the probation work and the pre-prosecution investigation by revising the probation law. In other words, the pre-sentencing investigation system and the sentencing investigation system should be separated.