PURPOSE: To have an automatically temp. controlled heater with the number of parts reduced and in simplified control mechanism by connecting in series a plurality of oxide superconductor with different critical temps.

CONSTITUTION: Resistance of each heater is represented by R, and the current by I. The critical temp. of heater 3-1 shall be 10°C, 3-2 20°C, 3-3 30°C, and the heater 3-4 be -30°C which is below normal service temp. This is to prevent the circuit from being broken, as the whole being put in superconductive condition at the time a switch 2 turned on should cause flow of a very large current. Because the whole is in normal conductive condition when the ambient temp. is 35°C, the total resistance becomes 4R to present that I35=V/4R, P35=V2/4R. When the ambient temp. is 25°C, on the other hand, only the heater 3-3 becomes in superconductive condition to result in a total resistance of 3R to present that I25=V/3R, P25=V2/3R. When the ambient temp. is 15°C, 5°C, in the same manner, it is presented that P15=V2/2R, P5=V2/R. That is, the amount of heat emission increases with lower ambient temp.