A lens barrel includes a non-rotatable annular ring and a circumferential guide groove; a first rotatable ring supported inside the annular ring and including a rotation-guiding projection slidably engaged in the circumferential guide groove; a second rotatable ring which rotates with the first rotatable ring and is only axially movable relative to the first ring, including an engaging projection slidably engaged in the circumferential guide groove with the rotation-guiding projection, wherein the engaging projection is insertable/removable from the circumferential guide groove through the insertable/removable aperture at a first assembling/disassembling angular position; and a coupling ring which is positioned inside the first and second rotatable rings. A coupler provided between the coupling ring and the second rotatable ring is disengaged at a second assembling/disassembling angular position. The first and second assembling/disassembling angular positions are substantially the same.