An axial-flow gas turbine engine includes a plurality of inlet guide vanes (V) which are radially disposed in an annular gas passage defined between an inner peripheral wall (Ch) and an outer peripheral wall (Ct) of a turbine. The inner peripheral wall (Ch) of the gas passage includes inner peripheral concave portions (Cc1 and Cc3) on an upstream side, and inner peripheral convex portions (Cv1 and Cv3) on a downstream side. The outer peripheral wall (Ct) of the gas passage includes outer peripheral convex portions (Cv2 and Cv4) on an upstream side, and outer peripheral concave portions (Cc2 and Cc4) on a downstream side. Therefore, a pressure difference in a radial direction of the inlet guide vane V is reduced or partially reversed, and a secondary flow toward an inner side in the radial direction can be suppressed to reduce pressure loss.