Apparatus for carrying out a vapour refrigeration process comprising a motor-operated main compressor which is equipped to suck in a mass flow of a fluid which serves as a refrigerant and is at evaporating pressure level and to compress this mass flow to a high pressure level, a high pressure heat exchanger which is equipped to cool the mass flow of the fluid that is at a high pressure level, to increase a density and to reduce a temperature of the fluid, an expander which is equipped to expand the mass flow of the fluid coming from the high pressure heat exchanger to the evaporating pressure level in work-performing manner, an evaporator which is equipped to absorb heat so that the density of the fluid when going through the evaporator decreases and the temperature of the mass flow coming from the expander at evaporating pressure level and the temperature of the fluid being fed through the evaporator increase, a subcooler which is connected downstream of the high pressure heat exchanger and upstream of the expander, wherein fluid at intermediate pressure level in the counter-flow in the subcooler absorbs heat and thereby subcools the mass flow flowing through the subcooler which is at high pressure level, a high pressure compressor, which is equipped to compress the mass flow which is at intermediate pressure level and which is guided counter to the mass flow of the fluid at high pressure level flowing through the subcooler and to mix it before the high pressure heat exchanger with the mass flow coming from the motor-operated main compressor, characterized in that after the subcooler and before the expander the part of the mass flow of the fluid, which is at high pressure level, guided in counter-flow through the subcooler is arranged to be branched off and to be expanded by means of a high pressure regulating valve to an intermediate pressure level, in that the high pressure compressor is mechanically connected directly to the expander to compress exclusively the mass flow branched off before the expander, and in that by means of the high pressure regulating valve an expander mass flow is arranged to be regulated, wherein there can be freely set at the high pressure compressor a pressure difference and an intake volume corresponding to a supply on the expander side, in that upon closure of the high pressure regulating valve its pressure difference rises until the unit of the expander and the mechanically directly connected compressor stops, so that there is no longer an expander mass flow and as a result thereof the high pressure rises, and in that upon opening of the high pressure regulating valve the intermediate pressure rises until the expander is operating and the desired expander mass flow, high pressure and expander intake temperature are set. a motor-operated main compressor which is equipped to suck in a mass flow of a fluid which serves as a refrigerant and is at evaporating pressure level and to compress this mass flow to a high pressure level, a high pressure heat exchanger which is equipped to cool the mass flow of the fluid that is at a high pressure level, to increase a density and to reduce a temperature of the fluid, an expander which is equipped to expand the mass flow of the fluid coming from the high pressure heat exchanger to the evaporating pressure level in work-performing manner, an evaporator which is equipped to absorb heat so that the density of the fluid when going through the evaporator decreases and the temperature of the mass flow coming from the expander at evaporating pressure level and the temperature of the fluid being fed through the evaporator increase, a subcooler which is connected downstream of the high pressure heat exchanger and upstream of the expander, wherein fluid at intermediate pressure level in the counter-flow in the subcooler absorbs heat and thereby subcools the mass flow flowing through the subcooler which is at high pressure level, a high pressure compressor, which is equipped to compress the mass flow which is at intermediate pressure level and which is guided counter to the mass flow of the fluid at high pressure level flowing through the subcooler and to mix it before the high pressure heat exchanger with the mass flow coming from the motor-operated main compressor, characterized in that after the subcooler and before the expander the part of the mass flow of the fluid, which is at high pressure level, guided in counter-flow through the subcooler is arranged to be branched off and to be expanded by means of a high pressure regulating valve to an intermediate pressure level, in that the high pressure compressor is mechanically connected directly to the expander to compress exclusively the mass flow branched off before the expander, and in that by means of the high pressure regulating valve an expander mass flow is arranged to be regulated, wherein there can be freely set at the high pressure compressor a pressure difference and an intake volume corresponding to a supply on the expander side, in that upon closure of the high pressure regulating valve its pressure difference rises until the unit of the expander and the mechanically directly connected compressor stops, so that there is no longer an expander mass flow and as a result thereof the high pressure rises, and in that upon opening of the high pressure regulating valve the intermediate pressure rises until the expander is operating and the desired expander mass flow, high pressure and expander intake temperature are set.