To provide a fixing device for an electrophotographic image forming device with the durability and safety of which are improved.

The fixing device for electrophotographic image forming device is characterized in that it is provided with an inner pipe 214, the ends of which are tightly sealed in order to maintain a predetermined pressure and stores, in its internal space, a predetermined amount of actuating fluid, a heat generating part 213, which is disposed round the inner pipe 214 and generates heat, a power supply part 300, which is eclectically connected to the heat generating part 213 and supplies external power, a fixing roller disposed round the heat generation part 213, and end caps 217, which are disposed at both ends of the fixing roller 212, and in which each of the end caps 217 has a large diameter portion provided with an electrode electrically connected to the power supply part and a small diameter portion fitted into the corresponding end of the fixing roller by a locking means.