A lens cap device having a cap protecting device, an actuating device, and a lens cap. The cap protecting device has a protecting cap with a lens exposure hole. The actuating device has a push element and an actuating element. The push element is slidably disposed on the cap protecting device. One end of the actuating element is pivotally connected on the cap protecting device to form a pivot point. The actuating element and the push element are linked together. The lens cap is slidably mounted on the cap protecting device. The lens cap is pivotally connected with the other end of the actuating element. The lens cap is driven by the actuating element to cover or open the lens exposure hole.