To provide a stator vane segment having satisfactory cooling performance during operation under high temperature heat flux and high pressure.

A stator vane segment 38 includes an external wall, an internal wall, a pair of vanes 32, and a hook which positions the segment on an inner shell of a turbine, and they are integrally cast. The external wall and the internal wall are divided into partitioned chambers 68a to 68f, and the partitioned chambers 68a to 68f are divided into an internal chamber 76 and an external chamber 78 by impingement plates 74a to 74f. Cooling steam is introduced on the external wall, flows into the external chamber 78, and passes through holes of the impingement plates 74a to 74f for impingement cooling of the external wall by the steam. The steam flows through a cavity 94 of the vane 32 for impingement cooling of the vane and enters the partitioned chamber on the internal wall. The steam is directed towards the internal wall by the impingement plate on the internal wall for impingement cooling of the internal wall. The steam returns through the other cavity in the vane for further impingement cooling of the vane and flows into a steam discharge port.