An exemplary electronic device includes a housing, a left rail and a right rail assembled in the housing, and a holder assembled on the left and right rails and received in the housing. The holder can slide out from the housing for securing a functional module thereon. The holder includes a bottom plate glidingly assembled on the left and right rails, and front and rear plates both pivotally secured on the bottom plate. The front and rear plates are both elastically biased to rotate about the bottom plate. When the holder is at least partially received in the housing, the front and rear plates are in original closed positions. When the holder is almost totally slid out from the housing, the front and rear plates rotate about the bottom plate to be in open positions for providing resilience to secure the functional module.