A support apparatus (3) for supporting at least one neck mold (4) of a plastic container, the apparatus being adapted to be fastened to a lower surface of a rotating device (2) of an injection blow molding machine, said support apparatus comprising a pair of plates (5) defining a longitudinal axis (X), said plates (5) being adjacent to each other along the axis (X) and separable from each other transversely to said axis (X), and being kept adjacent in a normally closed state by elastic means (6); wherein each plate (5) is provided with at least one respective recess positioned so that, when the plates (5) of said pair of plates are in the normally closed state, at least two recesses are adjacent to each other along said longitudinal axis (X) so as to define a seat for a neck mold (4) comprising a pair of split molds (7), each split mold (7) being capable of being accommodated in a recess of a respective plate (5); a pair of side guides (8) transverse to said longitudinal axis (X), adapted to be fastened to said lower surface of the rotating device (2), each side guide (8) being adapted to support a respective end of the pair of plates (5) from the bottom; wherein the side guides (8) are provided with a respective locking system (9) for locking or unlocking the pair of plates (5) to/from said pair of side guides (8) so that, in an unlocking position, the pair of plates (5) can be extracted transversely to the axis (X) thereof by sliding on the side guides (8).