To provide an illuminator which makes efficient illumination possible by irradiating only the peripheral part of a patient's mouth with illumination light while preventing affording an uncomfortable feel to the patient in close-up photographing for dental treatment purposes.

The illuminator 10 freely attachably and detachably mounted on the circumference of a lens barrel 32 of a digital camera 30 includes a light guiding member 16 of a tapered shape converging toward the subject side. The light guiding member 16 has an irradiation surface 22 perpendicular to the central axis E of the lens barrel 32 and an inner peripheral surface 24 parallel to the central axis E. The illumination light emitted from a light source section 14 is reflected on the surface of a reflection member 18 and is guided while being diffused by the light guiding member 16. The light guiding member 16 respectively emits the illumination light from the irradiation surface 22 toward the direction approximately parallel to the central axis E exemplified by an arrow B and from the inner peripheral surface 24 toward the central axis E exemplified by the arrow A. Consequently, the illuminator 10 nearly evenly illuminates only the peripheral part of the patient's mouth in close-up.