PROBLEM TO BE SOLVED: To provide a medical device and phototherapeutic apparatus capable of performing a therapy of an entire therapeutic object region by a single irradiation by providing an irradiation range capable of covering the entire therapeutic object region.SOLUTION: A medical device 30 is inserted into a living body and irradiates the therapeutic object region with light to perform a therapy of the region. The medical device includes: a long medical device body 41 having at least one lumen 42 and 43； long light diffusers 44 and 45 inserted in the medical device body 41 so as to extend along the lengthwise direction of the medical device 41； and a long reflector 46 having a reflecting plane for reflecting the light. The medical device body 41 includes an optically transparent outer wall part 41o extending along the lengthwise direction, at least in a part of an outer wall. The light diffusers 44 and 45 include: irradiation means 44 for irradiating the therapeutic object region with light； and light receiving means 45 for receiving the light from the therapeutic object region, and are disposed at a position sandwiched between the reflecting plane and the transparent outer wall part, facing the reflecting plane and the transparent outer wall part.【課題】治療対象部位全体をカバー可能な照射範囲を備えることにより、一度の照射で、治療対象部位全体を施術可能な医療用具及び光線治療装置を提供する。【解決手段】生体内に挿入され、治療対象部位に光を照射して部位の治療を行う医療用具３０である。少なくとも一つのルーメン４２，４３を有する長尺の医療用具本体４１と、医療用具本体４１内に、医療用具本体４１の長尺方向に沿って延長するように挿通された長尺の光拡散体４４，４５と、光を反射させる反射面を備えた長尺の反射体４６を備える。医療用具本体４１は、外壁の少なくとも一部に、長尺方向に沿って延長する光学的に透明な透明外壁部４１ｏを備える。光拡散体４４，４５は、治療対象部位に光を照射する照射手段４４と、治療対象部位からの光を受光する受光手段４５と、を備え、反射面と透明外壁部とに挟まれた位置に、反射面及び透明外壁部に対向して配置されている。【選択図】図６
