The new hydraulic silencer called a "variable resonance-mode type side-branch" resonator has been developed by one of authors in the previous paper. This device can make up the desired plural resonance modes freely with a single closed-end tube configuration. This paper presents the optimum design method of the present silencer for a real hydraulic system. In order to attenuate the pressure pulsation effectively in a real hydraulic system, the insertion loss or the peak amplitude of pressure pulsation, which are both dependent on the wave propagation characteristics of all the circuit elements including the silencer, are used as the constraint condition in the optimum design method. The appropriateness of the present optimum design method and the pulsation attenuation capability of the present silencer are examined by the fundamental experiments in the test hydraulic systems equipped with every key circuit design factors of practical hydraulic systems. Further, it is shown that the present silencer, which was designed to attenuate the successive 1st∼3rd harmonics of fixed descrete-frequency pressure pulsation, has proven to be very successful also in application to a real hydraulic excavator for attenuation of audible noise as well as pressure pulsation of these harmonics.