To provide a method of restraining an oxidative deterioration from occurring in a high-molecular PTC composition when subjected to a thermal history, where the PTC composition is composed of a binder whose main component is a crystalline high-molecular composition and metal carbide as conductive powder mixed into the binder and kneaded together.

Transition metal functions as a catalyst to cause an oxidative deterioration to high-molecular compound, so that metal inactivating agent is added to the high-molecular compound. Even if a high-molecular PTC device, which is composed of the high-molecular PTC composition and electrodes formed on both the sides of the PTC composition, undergoes a thermal history as it carries out a switching operation repeatedly, the binder is protected against the oxidative deterioration, so that the binder is hardly increased in volume with the oxidative deterioration, and the high-molecular PTC composition varies less in resistivity at a room temperature.