A pitch-control system according to the present invention includes a cylinder support portion provided on a rotor hub, a support point thereof being located away from a front end face (unsupported end) of the rotor hub on the opposite side of the rotor hub; a decentered coupling point provided at a decentered location on a root-side end face of the wind turbine blade; and a cylinder that is installed so as to pass through the unsupported end of the rotor hub, a coupling portion that is provided on a portion that protrudes to the outer side from the unsupported end being coupled in a freely rotatable manner to the support point via a spherical joint, and a coupling portion that is on the inner side of the unsupported end being coupled in a freely rotatable manner to the decentered coupling point via a spherical joint.