24 and 25 wholly or partly occupy spaces of the stay vanes 12 13 further first and second oil supply conduits 26 27 fig3 and 4 are connected between the upper and lower oil chambers 24 25 through bearing portions 18 19 respectively in order to coolingly lubricate these bearings a return conduit 29 is connected between the upper and lower oil chambers 24 25 the return conduit 29 is provided with a pump 28 housed in one of the second set of stay vanes 21 to return the oil in the lower oil chamber 25 into the upper oil chamber 24 furthermore an overflow conduit 30 is connected between the upper and lower oil chamber 24 25 to directly introduce oil in the upper oil chamber 24 into the lower oil chamber 25 when the oil level of the upper oil chamber 24 exceeds a predetermined level such oil level is detected by a float switch 31 reference numeral 33 designates supporting arms extending from the outer casing 11 these arms 33 are mounted on additional supporting bases 32 39 with the structure since the lubrication oil chambers 24 25 are confined in the stay vanes 11 12 the oil conduits 26 27 29 and pump 28 confined in one of the stay vanes 21 are positioned in the flow path 23 defined between the inner and outer casings the elements are always cooled by the fluid flowing through the flow path 23 and therefore the lubricating oil is sufficiently cooled without employing a separate cooling subsystem further since the lubrication oil circuit is disposed in the tubular member by effective space.