Abstract: The invention relates to a method of active attenuation of machine directon pressure pulsations in the stock fed into the headbox (10) of a paper or board machine in such a way that the pressure pulsations in the stock are measured and the water flow to be fed into the stock is controlled on the basis of the results of the measurement. The volume available for the stock flow is controlled by means of water flow changes. Pressure variations achieved by volume variations are arranged substantially in opposition to the pressure variations to be attenuated thus attenuating the pressure variations in the stock. The invention also relates to an apparatus for carrying out the above method. The apparatus comprises a sensor (6) or a set of sensors, on the basis of whose output signal/signals a regulator (7) has been arranged to automatically control the water flow to be fed into the stock by an adequately fast valve arrangement (1) moved by the controlling element (2) of the regulator (7).