A collapsible lens barrel is provided, including a mechanism capable of reliably inhibiting rotation of a rotational barrel even if any impact is applied thereto, for example, due to a fall with the barrel being extended. When the rotational barrel is pressed upon a fixed member due to impact in defiance of the biasing force of a wave spring, a first engagement portion provided at a camera body-side end of the rotational barrel engages with second engagement portions provided on a subject-side surface of the fixed member, which locks rotation of the rotational barrel, thereby making it possible to prevent gears from being damaged, for example.