Embodiments of a zoom lens barrel assembly for an imaging apparatus are provided. The zoom lens barrel has a simple structure and allows efficient space utilization in order to realize a compact size, which is currently required for a mobile imaging apparatus. The zoom lens barrel assembly can stably endure external impacts, provide more precise zoom operations, and stably operate for a long time without a malfunction of a zoom motor, which acts as a drive source. The zoom lens barrel assembly can increase the rotation gain of a driving source and improve space utilization inside a basic skeletal structure of a frame by modifying the structure of a gear train, which cooperatively connects the driving source and a rotary cam member.