Power transmission apparatus with an input for connecting to a drive unit which can be operated at a constant rotational speed, and at least one output for connecting to a mobile machine which can be operated at a variable rotational speed, comprising: - a hydrodynamic rotational speed/torque converter which is configured as a counter-rotating converter with at least one pump impeller, a turbine impeller and a diffuser which form a working space which can be filled with operating medium; - a superimposition transmission with at least one planetary gear mechanism, comprising an internal gear, a sun gear and a planetary carrier with a plurality of planets as elements of the planetary gear mechanism, the input of the power transmission apparatus being connected at least indirectly, preferably directly, to the pump impeller of the counter-rotating converter and to a first element of the planetary gear mechanism, the turbine impeller of the counter-rotating converter being connected at least indirectly, preferably directly, to a second element of the planetary gear mechanism, and a third element of the planetary gear mechanism being connected at least indirectly to the output of the power transmission apparatus or forming the said output; characterized by the following features: - the counter-rotating converter can be emptied; - with a switchable variable-speed coupling (20, 16) for transmitting the power in a first rotational speed range in the case of an emptied counter-rotating converter between the input and the output of the power transmission apparatus; - with a device for the at least indirect supporting and/or fixing of the second element of the planetary gear mechanism, in particular the connection between the turbine impeller of the counter-rotating converter and the second element of the planetary gear mechanism in the said first rotational speed range. - a hydrodynamic rotational speed/torque converter which is configured as a counter-rotating converter with at least one pump impeller, a turbine impeller and a diffuser which form a working space which can be filled with operating medium; - a superimposition transmission with at least one planetary gear mechanism, comprising an internal gear, a sun gear and a planetary carrier with a plurality of planets as elements of the planetary gear mechanism, the input of the power transmission apparatus being connected at least indirectly, preferably directly, to the pump impeller of the counter-rotating converter and to a first element of the planetary gear mechanism, the turbine impeller of the counter-rotating converter being connected at least indirectly, preferably directly, to a second element of the planetary gear mechanism, and a third element of the planetary gear mechanism being connected at least indirectly to the output of the power transmission apparatus or forming the said output; - the counter-rotating converter can be emptied; - with a switchable variable-speed coupling (20, 16) for transmitting the power in a first rotational speed range in the case of an emptied counter-rotating converter between the input and the output of the power transmission apparatus; - with a device for the at least indirect supporting and/or fixing of the second element of the planetary gear mechanism, in particular the connection between the turbine impeller of the counter-rotating converter and the second element of the planetary gear mechanism in the said first rotational speed range.