A HDD retaining mechanism includes a frame and a vibration isolator. The frame includes a through hole in a prescribed position. The vibration isolator includes a smaller cylindrical portion formed so as to be fitted in the through hole. The smaller cylindrical portion includes projecting portions formed by splitting one end portion of the smaller cylindrical portion into a plurality of portions in a circumferential direction. The projecting portions project into the accommodation space and abut against a HDD when the smaller cylindrical portion is fitted in the through hole. Each of the projecting portions includes a notch part recessed toward a center position of the smaller cylindrical portion from an outer circumferential surface of the cylindrical portion and extending across each of the projecting portions in the smaller circumferential direction of the cylindrical portion.