A platform cooling structure for a gas turbine moving blade is provided which is capable of improving cooling performance of a platform and of improving reliability of a moving blade in such a manner that a portion in the vicinity of a side edge of the platform which is away from moving blade cooling passageways and is easily influenced by thermal stress caused by high-temperature combustion gas, that is, an upper surface of the side edge is effectively cooled by guiding high-pressure cooling air, flowing to the moving blade cooling passageways, to a discharge opening formed in a surface of the platform in the vicinity of the side edge of the platform without particularly attaching an additional member such as a cover plate to the platform. A moving blade cooling passageway 17c is formed in the inside of the gas turbine moving blade. Cooling communication holes 24a and 24b, of which one ends communicate with the moving blade cooling passageway 17c and the other ends communicate with a plurality of discharge openings 22 provided in the surface of the platform in the vicinity of the side edge of the platform 5, are formed through the inside of the platform.