The earth potential difference (EPD) signals have been observed continuously to monitor the naturally induced earth current together with some meteorological elements at Sado island in the Japan Sea. All these signals were transferred into digital recorded data with 1 s sampling time over one winter season. The EPD signals have no variation in a period of no wind, however, multi-trained pulse signals are observed in a period of strong wind. It is revealed that like this EPD variations occur when the wind speed exceeds the threshold value of 20 m/s. The streaming potential effect might be generated under the ground caused by strong wind over the ground surface.