Abstract: A method of automatically cutting off high temperature and high current, includes calculating an FET voltage applied to an FET (Field Effect Transistor), based on a resistance of a CTS (Critical Temperature Switch) and a reference resistance, comparing the FET voltage with a predetermined threshold voltage, and setting the FET to an ON state when the FET voltage is higher than the threshold voltage and setting the FET to an OFF state when the FET voltage is lower than the threshold voltage. The CTS is a switch including an MIT (Metal-Insulator Transition) device. The MIT device has a metallic property only in a predetermined temperature range.