Main electrodes 3, 4 are formed on the inner surface of a flexible insulating sheet 2 along opposed edges thereof, and junction electrode sections 3a, 4a are formed on the main electrodes at their central portions. Comb-toothed sub-electrodes 7, 8 extend from the main electrodes 3, 4 into interdigitated relation, and a layer of electrically resistive material 9 is formed over the main and sub-electrodes. Electrically conductive paths 5, 6 are formed on the inner surface of a terminal mounting substrate to which terminals are attached, and one ends of the conductive paths 5, 6 are connected with the corresponding junction electrode sections 3a, 4a while the other ends thereof are connected with the terminals to be connected to a power supply. The terminal mounting substrate with the terminals is bonded to the insulating sheet.