The present invention relates to a zoom lens mount assembly for use in optical apparatus such as photographic camera, video camera or the like. The zoom lens mount assembly of this type usually comprises a plurality of frames consisting of a stationary frame and movable frames assembled into a multilayered frame structure. The present invention provides a novel and improved zoom lens mount assembly in which the innermost layer is constructed from a plurality of frames into a single-layered structure and thereby an inner diameter of the lens mount assembly is dimensioned as largely as possible without making the lens mount assembly as a whole bulky. The present invention also permits the cam frame to be molded of synthetic resin material or the like and permits this cam frame to be mounted in a bayonet fashion.