An abnormal vibration detection unit which is capable of stopping a wind turbine generator when excessive vibration is detected. The vibration detection unit has first and second acceleration detectors, a calculation device, a filtering relay, and a safety system which performs an emergency stop of the wind turbine generator in accordance with an output terminal of the filtering relay. The filtering relay has a filter circuit to extract a frequency component from the second analog output signal. The calculation device generates a predicted value of the output signal of the filter circuit part, and detects a failure of the first and second acceleration detectors or the filter circuit part by comparing the predicted value of the output signal of the filter circuit part with a measured value of the output signal of the filter circuit part received from the filtering relay.