An atmosphere conditioning device for testing combustion engines, comprising the device: - an inflow conduit arranged for being connected at a first end to a combustion engine admission to be subjected to testing and drawing in airfrom the outer atmosphere through a second end; - an outflow conduit arranged for being connected at a first end to the exhaust of the combustion engine and expelling exhaust gases into the atmosphere through a second end; - a first communication conduit which communicates the inflow conduit with the outflow conduit close to their respective first ends (1a, 3a), such that the admission of the device is in communication with the exhaust thereof; - a supercharging turbogenerator arranged in the inflow conduit, the turbogenerator comprising a turbine coupled to a dissipation system for dissipating the energy generated in the expansion; characterized in that it further comprises: - a bypass valve which diverts the air flow in the inflow conduit that circulates towards the turbine, the bypass valve and the turbine being able to be regulated to obtain desired pressure and air flow values in the inflow conduit; - a first heat regenerator, consisting of respective heat exchangers (15, 15') in the outflow conduit and in the inflow conduit connected by the same heat transfer fluid circuit, arranged between the supercharging turbogenerator and the first communication conduit, facilitating indirect heat exchange between the exhaust gases in the outflow conduit and the admission air in the inflow conduit; - a bypass valve in the outflow conduit together with the corresponding heat exchanger of the first heat regenerator, regulating the amount of exhaust gases that actually participate in the heat exchange; - a heat exchanger in the outflow conduit downstream from the first heat regenerator to cool the exhaust gases to a safe temperature; and - a turbocompressor downstream from the heat exchanger, charged by turbocompressor charging means, to regulate, together with the turbine and the bypass valve, the decrease in admission air pressure and admission air flow; and further characterized in that it allows connecting the admission of the engine to the second end of the outflow conduit and the exhaust of the engine to the second end of the inflow conduit, such that the operation of the device is inverted, the inflow conduit becoming the outflow conduit and vice versa, such that the turbocompressor, the turbine and the bypass valve together regulate the increase in admission air pressure. - an inflow conduit arranged for being connected at a first end to a combustion engine admission to be subjected to testing and drawing in airfrom the outer atmosphere through a second end; - an outflow conduit arranged for being connected at a first end to the exhaust of the combustion engine and expelling exhaust gases into the atmosphere through a second end; - a first communication conduit which communicates the inflow conduit with the outflow conduit close to their respective first ends (1a, 3a), such that the admission of the device is in communication with the exhaust thereof; - a supercharging turbogenerator arranged in the inflow conduit, the turbogenerator comprising a turbine coupled to a dissipation system for dissipating the energy generated in the expansion; - a bypass valve which diverts the air flow in the inflow conduit that circulates towards the turbine, the bypass valve and the turbine being able to be regulated to obtain desired pressure and air flow values in the inflow conduit; - a first heat regenerator, consisting of respective heat exchangers (15, 15') in the outflow conduit and in the inflow conduit connected by the same heat transfer fluid circuit, arranged between the supercharging turbogenerator and the first communication conduit, facilitating indirect heat exchange between the exhaust gases in the outflow conduit and the admission air in the inflow conduit; - a bypass valve in the outflow conduit together with the corresponding heat exchanger of the first heat regenerator, regulating the amount of exhaust gases that actually participate in the heat exchange; - a heat exchanger in the outflow conduit downstream from the first heat regenerator to cool the exhaust gases to a safe temperature; and - a turbocompressor downstream from the heat exchanger, charged by turbocompressor charging means, to regulate, together with the turbine and the bypass valve, the decrease in admission air pressure and admission air flow;