In a delivery apparatus in a machine for preparing hollow vessels by delivering mandrels supporting thereon preforms and vessels through a preform-heating zone and a draw-blow-forming zone, the downward movement of a mandrel-clamping mechanism is utilized for insertion of a preform into the mandrel and the rising movement of the clamping mechanism is utilized for withdrawal of a formed vessel. By this arrangement, insertion and fixation of preforms into mandrels and withdrawal of formed vessels from mandrels can be performed continuously, assuredly and smoothly in one apparatus while saving the waste in the blow-forming operation. If the operation of reversing the clamping mechanism is added, any particular device need not be disposed for reversing preforms.