To cool a tip turbine effectively and also to improve cycle performance by inducing hydrogen gas bypassed through a heat exchanger from a cold hydrogen supply source into a tip turbine, and installing an inlet passage to cool this tip turbine.

At the time of a slow flight of an air turbo ram jet engine, a driving gas Hd heated and generated by way of a heat exchanging part is taken into a peripheral side gas passage 17b via a receiving part 21, driving a tip bucket 24. Simultaneously, a cooling gas Hc bypassed with the heat exchanging part is made to flow into a cooling hole 28 of the tip bucket 24 by way of a through hole 22 of the receiving part 21 and an inner circumferential side gas passage 17a, whereby this tip bucket 24 is film-cooled. In addition, a part of the cooling gas Hc induced into the inner circumferential gas passage 17a is emitted to the inner circumferential side gas passage 17a by way of a bucket side gas passage 25 of the tip bucket 24. The cooling gas Hc passed through a bucket side gas passage 24 is reemitted to the inner circumferential side gas passage 17a by way of a bucket side gas passage 27. With this constitution, the tip bucket 24 and the tip stator blade 26 are cooled.