Light irradiation device

A light irradiation device comprising:

• a balloon formed from a light transmissive material;
• and a tubular body arranged inside the balloon and including a lumen through which a light irradiation body including a light irradiation unit is inserted, wherein the balloon includes a light transmissive window portion that transmits light from the light irradiation unit and a light shielding body that is disposed in a region other than the light transmissive window portion and has a lower transmittance of light from the light irradiation unit than a transmittance of the light transmissive window portion, the light transmissive window portion including a first end portion on a distal side in a major axis direction of the balloon and a second end portion on a proximal side in the major axis direction of the balloon, and the lumen of the tubular body includes a boundary portion on which a distal end of the light irradiation body abuts, at a position on the distal side of the first end portion and on the proximal side of a most distal end of the balloon.