<p>An object is to provide a cylinder driving device of a wind-power generation system capable of appropriately controlling a pitch angle of each rotor blade at a time of power failure with a simple configuration. The present invention achieves the object by including a piston connected to the rotor blade; a cylinder that moves the piston by a hydraulic pressure; an urging member that urges the piston in one direction; an accumulator that is connected to the cylinder, and supplies hydraulic oil urging the piston in an opposite direction to a direction where the piston is urged by the urging member to the cylinder; and an on/off valve that controls opening or closing of a channel between the accumulator and the cylinder.</p>
