Ablation method

1. An ablation method comprising:

a step I of observing an ablation target region in a tissue of a subject and a conservation region that should not be ablated, the conservation region being adjacent to the ablation target region, using observation means;

a step II of placing a heat monitoring instrument that deforms if a temperature thereof exceeds a predetermined temperature, in a boundary between the ablation target region and the conservation region under the observation using the observation means, the heat monitoring instrument including a locking portion that engages with a tissue in the boundary when the temperature of the heat monitoring instrument is equal to or below the predetermined temperature, and deforms and thereby disengages from the tissue when the heat monitoring instrument is heated from the temperature that is equal to or below the predetermined temperature to a temperature exceeding the predetermined temperature;

a step III of heating the ablation target region using an ablation instrument while observing the ablation target region using the observation means, a tensile force that pulls the heat monitoring instrument from the tissue toward an outside of a body of the subject being applied to the heat monitoring instrument; and

a step IV of stopping the heating at a stage where deformation of the heat monitoring instrument is confirmed based on detection of reduction or loss of the tensile force applied to the heat monitoring instrument.

2. The ablation method according to claim 1 , wherein the step III, the tensile force is applied to the heat monitoring instrument by a surgeon or an assistant for the surgeon via fingers thereof.