A small-volume push-push apparatus for mounting and demounting a hard disk includes a pressing member, a bracket, and an elastic rod. The bracket defines first to fourth sliding slots, and the elastic rod includes a sliding portion. The pressing member can drive the sliding portion to slide along the first to fourth sliding slots in sequence. When the sliding portion slides to an ending point of the first sliding slot and intersects with the second sliding slot, the bracket can move at a first direction. When the sliding portion slides to a starting point of the first sliding slot away from the fourth sliding slot, the bracket can move in a second direction opposite to the first direction.