This paper proposes a novel method to cleanse electric contacts in a digital input system with low power consumption, which is suitable for industrial computer systems such as substation control systems. Oxygenated membrane on the surface of the contacts is kept away by generating small arcs when the contacts open or close. In order to reduce power consumption, the state of the contacts has to be monitored at low current. On the other hand, high current is needed to generate arcs. Our circuit can solve the problem by only supplying enough the current to generate arcs when the contact has been opened or closed. The mechanism to generate arcs is clarified experimentally and analytically, and it is shown by simulation that the proposed circuit can generate small arcs despite low power consumption.