An illumination apparatus includes lenses, a first casing that has a radiation plane provided with annularly arranged windows for attaching the lenses, respectively, independently, and that has an opening at a position opposite to the radiation plane, and a first substrate associated with each of the lenses and accordingly disposed. The first substrate has at least one light emitting device mounted thereon. The first casing includes a holding portion associated with each of the windows. The holding portion each permits the lens to be attached to the first casing from a side thereof having the opening and also restrains the lens from moving through the first casing toward the radiation plane, and when the lens is attached to the first casing, the lens has an optical axis in a direction having a predetermined angle relative to a center axis of the first casing.