A lens activating device includes at least one elastic piece, at least one stationary piece and a movable piece. At least one elastic piece has at least four sheet portions and four sets of elastic portions. Each set of the elastic portions are serpentine and connected between two sheet portions in order to make the at least one elastic piece form a closed ring. The stationary piece is connected to two sheet portions, and the movable portion is connected to the other two sheet portions. The elastic force generated by the four sets of elastic portions exerts a restoring force on the movable piece. Via this arrangement, the slight rotation of the movable piece within the lens activating device can be reduced. Further, the problem that the elastic piece may scrape the neighboring elements can be prevented.