A lens device includes a main body unit, a guiding shaft unit, a lens unit, a focus adjusting unit and a resilient component. The guiding shaft unit includes three parallel guiding shafts disposed in the main body unit. The lens unit includes a lens frame disposed in the main body unit and having three guiding portions that receive slidably and respectively the guiding shafts, and a lens mounted co-movably in the lens frame. The focus adjusting unit is disposed in the main body unit and includes a driven member abutting against the lens frame and driven by a driving member for driving the lens unit to slide along the guiding shafts. The resilient component is disposed for biasing resiliently the lens frame toward the driven member.