The apparatus comprises a frame supporting two fixtures, of which at least one is movable, and which have respective crescents adapted to be brought together to form a circular profile engageable with the big end of a connecting rod and separable by an opening device for fracturing the big end of the connecting rod. The opening device comprises a pusher device which has a sloping surface and is slidably supported with respect to one of the crescents to abut against the other crescent, and a driving member, which is slidable transversely to the pusher device under control of driving elements, and has a sloping surface that is adapted to cooperate with a camming action with the sloping surface of the pusher device.