A living tissue bonding system including: a sandwiching section for sandwiching living tissue; a power source for supplying to the living tissue treatment energy for bonding the living tissue sandwiched by the sandwiching section; a temperature measuring section for measuring a temperature of the living tissue sandwiched by the sandwiching section; a calculation section calculating, from the temperature of the living tissue measured by the temperature measuring section and a time period of applying the treatment energy, a time integral value of the temperature of the living tissue; a comparison section comparing the time integral value of the temperature of the living tissue calculated by the calculation section with a predetermined setting value; and an instruction section giving an instruction based on a result of the comparison by the comparison section.