PURPOSE: To control a vibrating machine stably, by modifying the stress level while comparing the vibration load detected from a load detector with a aimed stress waveform, and outputting a modified stress waveform signal simultaneously from each vibrating machine.

CONSTITUTION: The load detectors 4W6 for detecting vibration load applied to a test piece T by the vibrating machines 1W3, are provided to the machines 1W3 respectively. The detected signals of the detectors 4W6 are inputted, and compared with the aimed stress waveform applied to the piece T by the machines 1W3, the modified stress waveform signal is obtained so that the stress level is modified equal to the aimed stress waveform, and a control device 7 for outputting the signal to the machines 1W3 simultaneously is provided. In this way, fatigue test can be performed while always applying the vibration load having stress waveform of a fixed stress level.