Abstract: A stirling cycle engine including a working piston defining a working chamber, a crankshaft located in a crankchamber, a connecting rod connecting the working chamber with the crankshaft, the connecting rod being passed through intermediate members. A gas seal structure is provided in the intermediate members around the connecting rod, the gas seal structure including a first oil chamber and a second oil chamber, the second oil chamber being located closer to the crankchamber than the first oil chamber, a resilient sealing ring disposed between the first and second oil chambers and having an outer surface tapered toward the crankchamber to reduce diameter thereof, a spring for biasing the sealing ring toward the crankchamber so that the outer surface of the sealing ring is urged to an opposing surface formed in one of the intermediate members.