PROBLEM TO BE SOLVED: To provide a diffusing optical fiber and an optical component for medical use that can apply light such as a laser beam uniformly in a large area.SOLUTION: A diffusing fiber 1 according to the present invention includes: an optical fiber 4 that has a core portion 2, and a cladding portion 3 surrounding the periphery of the core portion 2 and having a refractive index lower than that of the core portion 2 and a diffuser 5 of spherical or ellipsoid shape made of optically transparent materials, that is provided at one end of the optical fiber 4 and that has the refractive index equal to or higher than that of the core portion 2. The core portion 2 protrudes from the cladding portion 3 at one end of the optical fiber 4, and this protruded portion 2A is covered with the diffuser 5.
