A treatment system includes: a probe including an energy generator provided in the probe and configured to generate energy, and a treatment surface provided at a distal end of the probe and configured to apply the energy to a living tissue and a controller including a hardware, the controller being configured to: acquire a temperature of an outer surface of the probe other than the treatment surface sequentially store temperatures of the energy generator in association with times when the temperatures of the energy generator are acquired store a plurality of weighting factors calculated by experiment in advance in association with times going back from a current time to a past time and multiply the sequentially stored temperatures of the energy generator and the plurality of weighting factors for the corresponding times, perform integration, and estimate the temperature of the outer surface.
