A lens device includes a fixed lens, a rotatable lens barrel, and a base. The fixed lens includes at least one cam groove which has an opening portion. The rotatable lens barrel is sleeved within the fixed lens. The rotatable lens barrel includes at least one cam follower. The cam follower enters the cam groove through the opening portion and moves along the cam groove. The base is assembled to the fixed lens. The base includes at least one protruding structure. The protruding structure extends to the cam groove through the opening portion.