Abstract: A testing device is provided for performing four-point fatigue strength tests of a sample by applying alternating bending stresses to the sample. The device includes four rotary joints. Each rotary joint includes a pair of individual, spaced-apart rollers so that a sample can be guided between the individual rollers of the respective pairs of rollers. Each roller is rotatable about its own longitudinal axis. First and second plates are adapted to be fixed in a force introducing machine so that they are relatively movable toward and away from one another. Four holders are provided, each for supporting a respective one of the rotary joints. Two of the holders are mounted to the first plate, with the third and fourth holders being disposed between the two holders and being mounted to the second plate. Each holder mounts its rotary joint so that the individual rollers of the rotary joint are rotatable about a common rotation axis.