The present invention relates to a decompression-compensating instrument for use in intraocular surgery, wherein a perfusate is supplied to an affected part of an eye via a supply channel at a predetermined pressure, and the perfusate is aspirated via an aspiration channel together with the affected tissues that are to be removed, the decompression-compensating instrument supplying the perfusate into the affected part when the internal pressure of the affected part is excessively lowered, and being constructed so as to be connectable to a point midway along the supply channel and comprising a storage-member that forms a chamber that is closable except for an opening from which the perfusate to be supplied to the supply channel flows, the capacity of the storage member being 7 cm.sup.3 to 22 cm.sup.3.