In order to decrease friction coefficient of DLC (Diamond-like Carbon) film by external action, we developed the method to apply electric discharge during friction. To realize electric discharge not penetrating DLC film, we made SUJ2 special ball which had two parts. One part was made for getting stable friction; the other one was made for making potential difference between two parts. In the case of friction between Si-DLC film and SUJ2 special ball in air, friction coefficient decreased to 0.04 instantly by discharging. But gradually friction coefficient increased, and finally it became as same value as Control's value.