Abstract: A light irradiation device having an elongated outer shape includes: an optical fiber for emitting light from its distal end, which has a curved part, in which the distal end is oriented in a direction intersecting with a longitudinal direction of the light irradiation device by the curved part; and a light transmitting holder that retains a shape of the curved part of the optical fiber. The optical fiber has a core, or has the core and an outer surface layer, and the holder has a refractive index smaller than a refractive index of the core or a refractive index of the outer surface layer of the optical fiber.

Abstract: A light irradiation device including an optical fiber and a light transmissive optical path changing member for changing an optical path of light entering from the optical fiber, disposed on a distal side relative to the optical fiber. The optical path changing member includes a proximal side member disposed on a proximal side of the optical path changing member and a distal side member disposed on a distal side of the optical path changing member. The proximal side member and the distal side member are in contact with each other to form a boundary surface, and the boundary surface is inclined relative to a vertical plane of a central axis of the optical fiber.

Abstract: A light irradiation device having an elongated outer shape includes: an optical fiber for emitting light from its distal end, which has a curved part, in which the distal end is oriented in a direction intersecting with a longitudinal direction of the light irradiation device by the curved part; and a light transmitting holder that retains a shape of the curved part of the optical fiber. The optical fiber has a core, or has the core and an outer surface layer, and the holder has a refractive index smaller than a refractive index of the core or a refractive index of the outer surface layer of the optical fiber.

Abstract: A light irradiation device having an elongated shape is inserted into a catheter. The light irradiation device includes a light irradiation portion provided on a distal end side of a light irradiation device for outputting irradiation light to outside, and a large diameter portion positioned distal to the light irradiation portion and having an outer diameter larger than an outer diameter of the light irradiation portion.

Abstract: A catheter includes a long tubular main body, a window on a side of the main body and transmits light in a predetermined outward direction, and an opening on the side of the main body, the opening being configured to release a fluid. A direction in which the fluid is released from the opening intersects the predetermined outward direction in which light is emitted from the window.

Abstract: A light irradiation system for medical use includes a catheter having an elongated tube shape and a light irradiation device having an elongated shape and configured to be inserted into the catheter. The catheter includes a light transmitting portion provided at least in a part of a side surface on a distal end side of the catheter and configured to transmit light inside the catheter to outside of the catheter, and a first marker portion being radiopaque and being provided close to the light transmitting portion. The light irradiation device includes a light irradiation portion provided at least in a part of a side surface on a distal end side of the light irradiation device and configured to output irradiation light to the outside, and a second marker portion being radiopaque and being provided close to the light irradiation portion.

Abstract: A medical light irradiation device is provided with an elongated main body portion, a light irradiation portion, and a marker portion. The light irradiation portion is provided on one portion of a side surface on a distal end side of a main body portion, and irradiates light towards outside. The marker portion is provided on a distal end side of the main body portion, is radiopaque, and has a shape for identifying the location of the light irradiation portion in a circumferential direction when viewed from the outside.