The temperature rise of a wheel space between a high-pressure turbine and a low-pressure turbine is suppressed. Cooling air is led from outside a casing 17 to a wheel space via a low-pressure turbine initial stage stator blade 5 and a diaphragm 11. An upstream side space seal portion 41 is adapted to restrict and divide the upstream side space into an outer circumferential portion 25 and an inner circumferential portion 27 and to allow cooling air to the upstream side space outer circumferential portion 27 to blow out into the upstream side space outer circumferential portion 25. Also, a downstream side space seal portion 42 is adapted to restrict and divide the downstream side space into an outer circumferential portion 26 and an inner circumferential portion 28 and to allow cooling air to blow out into the downstream side space outer circumferential portion 26.