Applying ultrasound to hyperthermia treatment, the temperature rise caused by irradiation of focused ultrasound is discussed. A piezoelectric concave-shaped transducer whose radius of aperture is 100 mm, radius of concativity is 25 mm, and resonant frequency is 1 MHz is used. Glycerin is introduced as the phantom because of its transparency. The heat-sensitive tape which consists of thermometric ink covered with a Teflon thin film of 100 (mu)m in thickness is used. The tape is spread out on the phantom with an observation area 50 mm long and 8 mm wide. The tape indicates the temperature as the color differences. The spatial distribution of the local heat generation, especially surrounding the focal point, is observed as a function of irradiation time. The experiments are carried out in the same kind of transmission conditions. The theoretical analyses for both the spatial thermal distribution and the time profile of the temperature rise are estimated by using the heat equation. The observed results show good agreement with the calculated ones.