The present invention provides an overheat protection device which is capable of effectively preventing a secondary battery from overheating. In the overheat protection device (20), a variable resistive element(s) (11) of which resistance varies depending on a temperature is located on and thermally combined with a certain position(s) of an electrical system (1), and a switching element (15) for controlling a current depending on an applied voltage thereto is arranged so as to control the current flowing through the electrical system (1). When the certain position of the electrical system (1) comes to be under a high temperature condition, the variable resistive element (11) interrupts the current flowing through the electrical system (1) by changing the applied voltage to the switching element (15).