To prevent failure such as the deviation or the distortion of a lens caused by the expansion of air in a lens chamber formed between the lenses by forming a groove for ventilating between the lens chamber and the outside of the lens barrel on the inner peripheral surface of the lens barrel holding the lens.

The groove 52 in the optical axis direction is formed on the inner peripheral surface of a lens barrel main body 12 where plural lenses 14, 16 and 18 and distance rings 20 and 22 are disposed so as to ventilate between the lens chambers 54 and 56 between the respective lenses and the outside of the main body 12. Thus, when the respective lenses are attached in the main body 12, air resistance is reduced and the lens is easily attached. Even when temperature in the lens chamber rises and the air is expanded by the irradiation of ultraviolet rays in the case of attaching the lens 18 with ultraviolet curing adhesive, the lens does not receive strong pressure and the failure such as the float of the lens is prevented. Even when the air is expanded because of the temperature rise in the lens chamber due to a fire, etc., the deviation or the distortion of the lens is prevented.