A treatment device (100) for a medical treatment heats a biotissue at a desired temperature, and includes a treatment tool (120), a controller (170) and a storage section (123 187). The treatment tool includes a heat transfer portion (132, 134) which contacts with the biotissue to transfer heat to the biotissue, and a resistance element (140) 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 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 resistance value and the coefficient C1 and C2, and controls the temperature of the heat transfer portion by use of the calculated temperature.
