At current interruption by electric contact, a repetition phenomenon of arc extinction and re-ignition is often observed before complete extinction of arc discharge, in some cases for a long time and in other cases for a short time. Occasionally, no re-ignition is observed. From a viewpoint of arc duration, the period of this repeating arc is also an important factor, if it is very long. However, the conventional explanation about the contact arc duration excludes this repeating arc phenomenon so that it fails to explain the reason and the duration of this phenomenon. For the purpose of investigating why this phenomenon occurs and how long it lasts, the arc extinction current and the arc re-ignition voltage have been measured for tungsten electrode, palladium electrode, copper electrode, and silver electrode. The circuit is, for simplicity, resistive with a capacitor source voltage and a fixed short arc gap of 0.5 mm. Taking newly into account the idea of unstable arc region by the measured results, the conventional explanation was improved. As a result, the reason and the duration of arc extinction and re-ignition phenomenon have become understandable. For simplification, the main description is based on the results by tungsten electrode. The results by other electrodes are summarized in appendix.