A rotor craft comprising: a rotor shaft; a plurality of blades that rotate about the rotor shaft; a hub that couples the plurality of blades to the rotor shaft; and a plurality of torsion applying mechanisms, each torsion applying mechanism of the plurality of torsion applying mechanisms twisting a proximal end portion of a corresponding blade of the plurality of blades relative to a distal end portion of the corresponding blade about a center axis of the blade, wherein each blade of the plurality of blades includes: a spar constituted by a long shaft-shaped structural member, the spar including a proximal end portion that is connected to the hub; and a skin in which the spar is inserted, such that a distal end portion of the skin and a distal end portion of the spar are connected to each other, and such that portions of the skin other than the distal end portion are rotatable relative to the spar about a center axis of the spar, and the hub includes: a hub body mounted to the rotor shaft; and a hub arm that connects the spar to the hub body, characterized in that the spar has such a cross-sectional shape that, from a predetermined position in a longitudinal direction of the spar toward the distal end portion of the spar, a dimension of the cross-sectional shape in a forward-rearward direction and a dimension of the cross-sectional shape in an upward-downward direction increases gradually. a rotor shaft; a plurality of blades that rotate about the rotor shaft; a hub that couples the plurality of blades to the rotor shaft; and a plurality of torsion applying mechanisms, each torsion applying mechanism of the plurality of torsion applying mechanisms twisting a proximal end portion of a corresponding blade of the plurality of blades relative to a distal end portion of the corresponding blade about a center axis of the blade, wherein each blade of the plurality of blades includes: a spar constituted by a long shaft-shaped structural member, the spar including a proximal end portion that is connected to the hub; and a skin in which the spar is inserted, such that a distal end portion of the skin and a distal end portion of the spar are connected to each other, and such that portions of the skin other than the distal end portion are rotatable relative to the spar about a center axis of the spar, and a spar constituted by a long shaft-shaped structural member, the spar including a proximal end portion that is connected to the hub; and a skin in which the spar is inserted, such that a distal end portion of the skin and a distal end portion of the spar are connected to each other, and such that portions of the skin other than the distal end portion are rotatable relative to the spar about a center axis of the spar, and the hub includes: a hub body mounted to the rotor shaft; and a hub arm that connects the spar to the hub body, a hub body mounted to the rotor shaft; and a hub arm that connects the spar to the hub body, characterized in that the spar has such a cross-sectional shape that, from a predetermined position in a longitudinal direction of the spar toward the distal end portion of the spar, a dimension of the cross-sectional shape in a forward-rearward direction and a dimension of the cross-sectional shape in an upward-downward direction increases gradually.