A turbine casing includes a plurality of arc-shaped segments having a flange at each side end to connect to a flange of an adjacent arc-shaped segment. The flange extends outward from an outer surface of each arc-shaped segment and extends along the outer surface in a front-to-rear direction. Each arc-shaped segment has a portion of the outer surface that is co-linear with the flange in a front-to-rear direction that does not include the flange.