A treatment device for a medical treatment heats a biotissue at a desired temperature, and includes a treatment tool, a controller and a storage section. The treatment tool includes a heat transfer portion which contacts with the biotissue to transfer heat to the biotissue, and a resistance element into which power is supplied to heat the heat transfer portion. The controller is detachably attached to the treatment tool, and measures a resistance value R of the resistance element. The storage section stores a coefficient C2. The controller calculates a coefficient C1 based on a calibration temperature when the treatment tool is connected to the controller. The controller calculates a temperature of the resistance element using the R, C1 and C2, and controls the temperature of the heat transfer portion.
