In order to improve reliability of potentiometer, mechanism of output noise between sliding contact and resistor is investigated. As a result of analysis, abrasion dust is proved to behave as insulation because of the conductive carbon separation. Furthermore, adsorption of volatile from the components of potentiometer is proved to increase stickiness of abrasion dust. Therefore, noise is output when the contact brush steps over the abrasion dust. On the basis of the mechanism, reduction of abrasion dust amount and stickiness is found to effective to improve reliability of potentiometer.