PURPOSE: To maintain the pulsation reducing action of oil pressure by a pulsation damper regardless of the fluctuation of the pump rotating speed by fitting the pulsation damper with a mobile bulkhead dividing the interior into two to change the volume near a discharge port, and moving the bulkhead in response to the pump rotating speed.

CONSTITUTION: A pulsation damper 2 is fitted to a hydraulic pipe near a discharge port in a hydraulic pump 1 applicable for the hydraulic system of an airplane, and an actuator 4 is connected on its downstream side. A bulkhead 2a dividing the interior of the pulsation damper 2 into two is movably inserted in it. The position of the bulkhead 2a is controlled by a control device 3, and the control device 3 generates a control signal to change the volume of the pulsation damper 2 and minimize the fluctuation when the fluctuation amplitude of the discharge oil pressure is a fixed value or above based on the data regarding the oil pressure from a pressure sensor 5.