A zoom lens barrel includes a linear guide ring; a moving frame having a male helicoid; a rotatable ring coupled to the linear guide ring; a female helicoid formed on the rotatable ring, and engaged with the male helicoid; a switching ring coupled to the rotatable ring; a switching member; and a switching-member moving groove including a first inclined section, a switching section, a second inclined section and an assembling section. The lead angle of the first inclined section is the same but has an opposite inclination to that of the female helicoid. The follower projection is inserted in the first inclined section. The switching section extends parallel to the optical axis. The second inclined section extends parallel to the first inclined section. The assembling section extends rearwards from a front end of the second inclined section to be parallel to the optical axis.