A thermal sensor that includes a ceramic body formed of NTC thermister ceramic, heat sensing part electrodes, temperature compensation part electrodes, external electrodes, and a cavity. A heat sensing part, which is the surface layer of the ceramic body, is heated by, for example, radiant heat transfer, reducing the resistance value of a thermister ceramic layer between the heat sensing part electrodes. Since the heat of the heat sensing part of the ceramic body is insulated by the cavity and thus prevented from diffusing, the heat capacity of the heat sensing unit is reduced, obtaining high sensitivity and high responsiveness.