The importance of research on the investment security of the state to prevent hazards and overcome existing threats in this area is growing significantly in modern conditions. Despite significant scientific research on this issue, one of the main problems in the investment security system of the state remains the provision of financial resources for capital investments on the scale of the national economy. Therefore, the purpose of the article is to reveal the role of capital investment as a basic prerequisite among the main elements of the state’s investment security system to develop the mechanism of its provision further. To achieve the goal, the authors used such methods and techniques of the theory of cognition as analysis and synthesis, comparison, statistical analysis, and a systematic approach. The genesis of the concept of economic security in the views of Ukrainian scientists has been studied. Threats and indicators of Ukraine's investment security have been identified. The basic elements of the investment security system of the state were revealed. The conducted research proves that the mechanism of ensuring investment security of the state is based on retrospective indicators, therefore it allows to react to adverse or crisis conditions of the economy with a delay. To guarantee the investment security of the state in the current regime, it is necessary to focus efforts on ensuring its prerequisites. After all, these prerequisites make it possible to preemptively guarantee the state of the economic system, which is resistant to the influence of internal and external factors that create threats even before their manifestation. The most critical for Ukraine from the list of prerequisites for investment security are the availability of financial resources for capital investments and an effective mechanism for transforming financial resources into capital investments. Prospects for further research are the development of an investment security mechanism, where a key role is assigned to depreciation policy at the national level in mobilizing financial resources to ensure the investment process.