A movable-blade operation system for a hydraulic machine according to an embodiment includes an oil hydraulic cylinder installed within a rotational shaft, a bidirectional pump, a pump drive motor, a control unit, and an oil head installed in the hydraulic machine. The bidirectional pump selectively feeds pressurized hydraulic oil to one of a first cylinder chamber and a second cylinder chamber. The oil head couples the rotational shaft rotatably, and the hydraulic oil fed from the bidirectional pump to the first cylinder chamber and the second cylinder chamber flows through the oil head. The bidirectional pump, the pump drive motor, and the control unit are installed outside the hydraulic machine.