Treatment system and actuation method for treatment system

A treatment system comprising:

• a power source;
• a controller configured to control the power source;
• a treatment instrument including a pair of grasping members configured to grasp a living tissue, and
• a heating element disposed on at least one of the pair of the grasping members, the heating element being electrically connected to the power source and configured to generate heat with power outputted from the power source;
• wherein the controller is configured to:
• repeatedly perform a control in a first control mode for controlling an output of the power so as to increase a temperature of the heating element to a first temperature and to keep the temperature of the heating element at the first temperature, and a control in a second control mode for controlling the output of the power such that the temperature of the heating element decreases,
• stop the output of the power based on at least one of a first result of a comparison between a time period for the temperature during one period in the first control mode or during one period in the second control mode of the heating element to reach a predetermined temperature and a preset threshold time period and a second result of a comparison between a rate of change in the temperature of the heating element during one period in the first control mode or during one period in the second control mode and a preset threshold rate;
• and
• control the output of the power such that the temperature of the heating element is kept constant at a second temperature lower than the first temperature in the second control mode.