PURPOSE: To reduce the number of parts and to reduce cost in a lens barrel provided with a photointerrupter by interposing the photointerrupter between the lens barrels and forming an elastic part pressing the photointerrupter to either lens barrel in the other lens barrel.

CONSTITUTION: This lens barrel is constituted by interposing the photointerrupter 10 between the lens barrels 5 and 7 and forming the elastic part 5C pressing the photointerrupter 10 to either lens barrel 7 in the other lens barrel 5. In the case of assembling the lens barrel, the photointerrupter 10 is dropped in the groove parts 7a and 7b of an afocal ring 7 being either lens barrel. Then, in the case of assembling the afocal ring 7 in the fixed lens barrel 5 being the other lens barrel, the photointerrupter 10 is pressed (negative pressure) and held on the wall surface of the groove parts 7a and 7b by the elastic part 5C formed in the lens barrel 5. Thus, a printed circuit board or the backing material of a main flexible lead wire for fixing the photointerrupter 10 and a screw and a positioning pin for fixing the printed circuit board or the like are not required, so that the degree of freedom in design is increased.