A high-frequency cauterization power source is an electrosurgical apparatus for joining biological tissues. The electrosurgical apparatus includes a high frequency power supply portion for supplying a high frequency power that is applied to biological tissues; a detection portion for detecting a voltage and a current of a high frequency power that is output from the high frequency power supply portion; a tissue impedance calculating portion that calculates an impedance of biological tissue based on respective values for voltage and current detected at the detection portion; and a control portion that controls so as to substantially stop supply of the high frequency power from the high frequency power supply portion based on whether or not an increase greater than or equal to a predetermined value in the impedance that is calculated at the tissue impedance calculating portion occurs two times.