A lens barrel 11 is mounted to a collapsible imaging device 1 having a zooming function and includes a cam frame 19, a first lens frame 39, a second lens frame 45, and a third lens frame 55. First, second, and third lens frame cam grooves 25, 27, 29, respectively including in the longitudinal direction thereof insertion parts 25a, 27a, 29a, collapse parts 25b, 27b, 29b, and variable power parts 25c, 27c, 29c are formed in the inner peripheral face of the cam frame 19. The third lens frame cam groove 29 are deeper than the first and second lens frame cam grooves 25, 27 and are intersected at the collapse parts 29c thereof with the respective insertion parts 25a, 27a.