A charge-control mechanism of CCA (Charge Control Agent) has been proposed in the present investigation that assumes an appreciable temperature increase at the “toner/carrier” interface due to the tribo-electrification. Further assumption is that CCA be present on the surface of both toner and carrier. Because of the present local heating, the electrical resistivity of CCA is remarkably decreased to give a conductive channel, through which the carrier-flow occurs effectively to charge up the toner. These two assumptions have experimentally been verified. Especially, the local heating up to around 100 °C has been confirmed by using a pigment-marker which changes its color from black to red. Around this temperature, the electrical resistivity of CCA is also found to be significantly lowered by three orders of magnitude as deduced from the temperature dependence of the electrical resistivity.