To prevent the damage of the normal tissue on the periphery of a lesion part even if an irradiation direction of energy deviates in accordance with the movement of a patient by detecting the irradiation direction of the energy in an insertion part, indicating the direction to an operator and detecting the irradiation direction of a control means for controlling thermotherapy.

A thermotherapeutic device 10 has a side irradiation type laser beam irradiation device 1 to be inserted into the living body and the laser beam introduced by an optical fiber 118 from the laser beam generator 2 is irradiated toward the vital tissue 20 from a housing 112. A rotating angle setting and rotating angle detecting section 120 is installed between a main body front part 110 and a main body rear part 111 to determine the irradiation direction of the laser beam emitted from a laser reflection part reflection surface 127. The deviation is detected by using the rotating angle setting and rotating angle detecting section 120 and if the deviation exceeding a permissible range occur, the therapy is interrupted and after the mispositioning is corrected, the therapy is restarted.