Drive device for an extrusion blow moulding machine for opening and closing a blow mould comprising two mould halves (12/v, 12/h) in the open state of which a tubular preform created by extrusion can be introduced into the blow region between the two mould halves (12/v, 12/h), wherein once the mould halves (12/v, 12/h) have been closed with the minimum closing force required for the blowing process, which holds the mould halves (12/v, 12/h) together in a sealing manner, the preform can be blown into the standard shape, wherein as soon as the blown hollow piece has achieved sufficient dimensional stability through cooling, the mould halves (12/v, 12/h) are separated from one another in order to remove the blown hollow piece, where appropriate following prior removal of protrusions (19, 21) of the extruded tube material that were squeezed out of the preform in the calibrating area and in the bottom region of a, for example, bottle-shaped hollow piece when closing the mould halves (12/v, 12/h), wherein the drive device is configured such that the mould halves (12/v, 12/h) are moveably guided on shared linear guiding elements (24/l, 24/r) and kinematically coupled to one another by means of a thrust reversing system such that, in the event of motion control by means of a drive unit engaging with one of the mould halves, they perform opposing translatory strokes, wherein a mould closing unit comprising the mould halves (12/v, 12/h) and the drive unit is arranged between substantially parallel limbs (51/v, 51/h) of a clamping fixture, one of which limbs forms a support for one of the mould halves and the other an abutment for the drive unit engaging with the other mould half., wherein the closing unit is supported on at least one of the parallel limbs (51/v, 51/h) by means of an elastically pre-stressed buffer element that can be pre-stressed to a restoring force corresponding to the closing force of the mould halves (12/v, 12/h), wherein the kinematic dead centre of the drive unit, viewed in the direction of the closing movement of the driven mould half (12/v, 12/h), lies beyond the closing stroke phase, from which point the mould halves (12/v, 12/h) are held together and supported, wherein the buffer element and the closing unit are adapted to each other in such a way that the pre-stress of the buffer element at the kinematic dead centre of the drive unit corresponds at least and approximately to the minimum closing force of the closing system, characterised in that the buffer element is formed as a double-acting hydraulic linear cylinder, the piston and housing of which are tightly connected, in a manner guaranteeing tensile strength, to one of the elements of the closing unit and the clamping fixture that are moveable relative to each other, wherein the first pressure chamber of the linear cylinder subjected to an increase in pressure during the closing operation can be communicatively connected to a pressure accumulator (96, 128, 131), which is pre-stressed to a pressure, the action of which on the piston surface of the linear cylinder results in a closing force counteracting the drive force, and characterised in that two pressure chambers (88, 121) are defined separately from each other in a pressure-tight manner by the piston, which are penetrated by piston rods (123,124) of different diameters, wherein a first piston rod is arranged on a side of the piston facing away from the closing unit and wherein a second piston rod tightly connects the piston to the clamping fixture and wherein the first piston rod has a larger diameter than the second piston rod and consequently an axially moveable annular surface of the piston delimiting a first pressure chamber is larger than the annular surface axially delimiting the second pressure chamber, and consequently, if the same pressure is injected into both pressure chambers (88, 121) a resulting force acts on the piston and the pressure chambers (88,121) can be communicatively connected to each another, or alternatively separated from each other, by means of a 2/2-way valve.