<p>By provision of self-correcting functions the operation point of the pump turbine (4) is monitored continuously, and actions are taken at a suitable time so as to prevent the operation point of the pump turbine (4) from falling into the hump characteristic region (Z) in accordance with approaching degree of the operation point to the hump characteristic region (Z). Even when water hammering phenomena from another hydraulic machinery sharing pipe lines is affected, the operation point of the pump turbine (4) is maintained without allowing any abnormal approach to the hump characteristic region (Z).</p>
