To provide an induction thermal fixing device constituted so that energy is more saved and the temperature of an electrical conductive member is efficiently raised by reducing leakage magnetic flux.

This fixing device 128 is provided with a fixed hollow electrical conductive temperature raising member 12 and a pressure roller 13 indirectly bringing a sheet 10 holding toner 11 into close contact with the raising member 12. Then, a flat part 21 for enlarging a nip area N is formed on the raising member 12. Besides, one part of a core 17 forming a closed magnetic circuit is inserted in the hollow part 12a of the raising member 12. By a coil 14 wound round so as to be interlinked with the core 17, the magnetic flux generating an induction current along in the circumferential direction of the raising member 12 is generated.