Hydrodynamic retarder

The invention relates to a hydrodynamic retarder device (1) comprising a stator (5) and a rotor (4), which can be coupled to a shaft (2) for braking operation. In order to provide a retarder device (1) in which the switchability of the rotor (4) is realized in the simplest possible manner and with minimal losses, a switchable freewheel (10) is provided between the shaft (2) and the rotor (4), which couples the rotor (4) to the shaft (2) in a locked state.