Hyperthermia is one of the modalities for cancer treatment, utilizing the difference of thermal sensitivity between tumor and normal tissue. In the treatment, tumor should be heated up to the therapeutic temperature between 42 and 45 degrees C. In Japan, large number of capacitive heating devices are employed for hyperthermic treatments. However, temperature distributions inside the patient body during the treatment have not been cleared. So, in this study, numerical calculations of temperature distributions inside patient body during the capacitive heating have been investigated. As a result, blood flow rate of a target tumor had a large influence to its temperature.