A study of clinical hyperthermia based on the soft heating method is described. A heating device made of temperature-sensitive Fe-P-C-Cr amorphous metal flakes was prepared and implanted into an agar phantom and in vivo. We measured the temperature distribution established in the phantom and the heating characteristics in vivo. In an animal experiment, a rabbit and a VX-2 tumor were used. The VX-2 tumor was transplanted into the rabbit's liver. The results of the experiment reveal that the heating device sufficiently heats the tumor when the temperature reaches 43°C under blood flow. This method has potential applications in a clinical context.