The objectives of the research are to identify and analyze the weaknesses of the public prosecutor's authority in a follow-up investigation of Illegal Deforestation cases, as well as reconstructing the authority based on the value of justice. The Research method used in this research are Juridical-Normative using the paradigm of constructivism where the research approach method used is socio-legal. The research data sources are analyzed using qualitative descriptive analysis. The findings show that the regulation of investigative authority by the public prosecutor in Law Number 18 of 2013 does not reflect the value of justice, because it has not regulated additional articles or explanations of the law and there are also no other rules that describe the conduct of investigations by public prosecutors, especially the forms of investigation activities in question so that it is feared to cause polemics or overlapping investigations. The clash of authorities will certainly result in delays in the legal process of handling Illegal Deforestation cases. Reconstruction of the value of the public prosecutor's authority in further investigations of Illegal Deforestation cases, that the author feels that law enforcement on forestry cases needs comprehensive action. Several key areas and approaches are needed by changing the regulations contained in the Law of the Republic of Indonesia Number 18 of 2013 concerning Prevention and Eradication of Illegal Deforestation in Article 29, and Article 42.