A plastic mold decapsuling apparatus for decapsuling a plastic mold by feeding an etchant to the plastic mold comprises an etchant bottle; an etchant tank; a decapsuling plastic mold holder; an etchant feeding pump; and, in particular, a bell-shaped cover cap for shielding a plastic mold to be decapsuled on the mold holder from outside air to maintain pressure of the etchant fed by the etchant feeding pump. Since the plastic mold is shielded, even if the plastic mold is decapsuled, it is possible to maintain the etchant feeding pressure at a constant level without introducing outside air into the etchant recirculating passage, thus permitting a stable decapsuling treatment.