The invention refers to a pressure compensating device (4) for a bearing housing, which is incorporating a sealed off compartment, and which device is intended to compensate pressure variations in the sealed off compartment, wherein the device (4) incorporates a housing (5, 6, 7), in which is positioned a bellows (9) of flexible material, which housing (4) has at least one first opening (10) through which the interior of the bellows (4) communicates with the side of the bearing housing where a varying pressure can be expected, and wherein the bellows (4) further is associated with an additional opening (8), adapted to allow the bellows (4) to alter its momentary form for compensating such pressure variations.