The paper formulates an understanding of the penal nature of the punishment, based on the essential aspect of the subject of the penal law and its positive impact on it. It is proved that the defining property of its subject is the public danger, serving the sentence of the convicted person. The provisions and norms of the penitentiary law, by means of which the convict is influenced, are corrective in nature. The proposed content of the legal nature allowed us to reveal the criterion of the system, the branch of law under consideration, the organic interrelation of its provisions and norms with solving problems and achieving goals. Such a criterion is the degree of public danger of a person serving a sentence imposed by the court, executed by the relevant criminal enforcement agencies. On the one hand, it materially "connects" the branch of law under consideration with criminal law, on the other, it gives them independence. The study of the problem of the penitentiary function of punishment, taking into account the revealed nature of its penitentiary, has made it possible to state that punishment is valuable in the system of provisions and norms of criminal executive law. All of this is aimed not at punishment, but at ensuring its serving and execution, within the framework of criminal-executive legal relations. At the same time, it is not punishment, but its essence in the form of a good, specified by the court's verdict by type, volume, time, is served and executed. The content of this process, its focus form a criminal-executive function, based on a certain degree of social danger of the convict. The "job" of the function is to stop the public danger of the convict as much as possible, creating the conditions for achieving the goal of the criminal executive legislation to correct the criminal.
