A light source apparatus includes a light source, an optical fiber, and a positioning mechanism. The positioning mechanism is configured with a planar position adjustment mechanism, an axial line position adjustment mechanism, and an orientation maintaining mechanism. The planar position adjustment mechanism adjusts a position of the optical fiber in a direction following the light-emitting surface. The axial line position adjustment mechanism adjusts the position of the optical fiber in a direction intersecting with the light-emitting surface. The orientation maintaining mechanism holds the optical fiber in a state where an axis direction of the optical fiber lies in a predetermined intersecting direction with respect to the light-emitting surface.