An object is to improve the buckling strength with respect to a load in the edge direction, to bring the safety factor for the buckling strength closer to the safety factor for the material strength, and to achieve a further reduction in weight. A wind-turbine rotor blade (5) has an outer skin member (11) formed of fiber-reinforced plastic, shear webs (15), and trailing-edge sandwich members (14) disposed closer to a trailing edge (18) than the shear webs (15) are. The outer skin member (11) at the dorsal side located closer to the trailing edge (18) than a trailing-edge end of the trailing-edge sandwich member (14) located at the dorsal side is or a vicinity of the trailing-edge end of the trailing-edge sandwich member located at the dorsal side is coupled, via a reinforcing member (19), with the outer skin member (11) at the ventral side located closer to the trailing edge (18) than the trailing-edge end of the trailing-edge sandwich member (14) located at the ventral side is or a vicinity of the trailing-edge end of the trailing-edge sandwich member located at the ventral side.