To provide a heat fusing heater capable of preventing a crack and break caused by the thermal stress of a base plate.

In the heat fusing heater 1 constituted in such a manner that a resistance layer (heating element) 2-a is arranged on a heater base plate 3-b, a metallic pattern 4-b made of a material having heat conductivity higher than that of the heater base plate 3-b is arranged on almost the whole of a surface opposite to the surface on which the resistance layer 2-a of the heater base plate 3-b is disposed. Thus, the temperature gradient of the heater base plate 3-b is made gentle, so that the thermal stress (thermal shock) applied to the heater base plate 3-b is suppressed smaller and the occurrence of the crack and break due to the thermal stress (thermal shock) of the heater base plate 3-b can be effectively prevented to enhance the durability of the heating/ fixing heater 1.