A moisture separator which separates moisture from moist steam, comprising: a plurality of corrugated plates (43, 53, 54) each having a zigzag cross-sectional shape with projections and depressions that are arranged alternately, said plurality of corrugated plates (43, 53, 54) being arranged at predetermined intervals to form a steam passage for the moist steam; and a plurality of collecting plates which are fixed to the corrugated plates (43, 53, 54), each of said collecting plates extending toward an upstream side in a direction of a steam flow within the steam passage so as to cover each of the projections of the corrugated plate (43, 53, 54), wherein between the collecting plate and each of the corrugated plates (43, 53, 54), a pocket section is formed with an opening which opens to the upstream side in the direction of the steam flow, wherein a drain duct section is provided on a downstream side of the pocket section in the direction of the steam flow and is in communication with the pocket section, said drain duct extending vertically, wherein the collecting plate is fixed to the corrugated plate (43, 53, 54) on a downstream side of the projection in the direction of the steam flow, and wherein, of a space formed between the collecting plate and the corrugated plate (43, 53, 54), an upstream portion and a downstream portion in the direction of the steam flow function as the pocket section and the drain duct section, respectively, characterized in that the moisture separator further comprises a drain plate which is provided between the collecting plate and the corrugated plate (43, 53, 54) to direct the moisture collected in the pocket section to the drain duct section, and in that the drain plate is arranged horizontally or is downwardly-inclined toward a downstream side in the direction of the steam flow. a plurality of corrugated plates (43, 53, 54) each having a zigzag cross-sectional shape with projections and depressions that are arranged alternately, said plurality of corrugated plates (43, 53, 54) being arranged at predetermined intervals to form a steam passage for the moist steam; and a plurality of collecting plates which are fixed to the corrugated plates (43, 53, 54), each of said collecting plates extending toward an upstream side in a direction of a steam flow within the steam passage so as to cover each of the projections of the corrugated plate (43, 53, 54), wherein between the collecting plate and each of the corrugated plates (43, 53, 54), a pocket section is formed with an opening which opens to the upstream side in the direction of the steam flow, wherein a drain duct section is provided on a downstream side of the pocket section in the direction of the steam flow and is in communication with the pocket section, said drain duct extending vertically, wherein the collecting plate is fixed to the corrugated plate (43, 53, 54) on a downstream side of the projection in the direction of the steam flow, and wherein, of a space formed between the collecting plate and the corrugated plate (43, 53, 54), an upstream portion and a downstream portion in the direction of the steam flow function as the pocket section and the drain duct section, respectively, characterized in that the moisture separator further comprises a drain plate which is provided between the collecting plate and the corrugated plate (43, 53, 54) to direct the moisture collected in the pocket section to the drain duct section, and in that the drain plate is arranged horizontally or is downwardly-inclined toward a downstream side in the direction of the steam flow.