This paper presents an approach to minimize weight of suspension parts while keeping the fatigue strength base on a non-parametric boundary shape optimization theory. As an index for the fatigue failure, we considered the frequency processing stress or strain in a suspension part evaluated from actual loading history. To avoid the irregularity coming from using the local value for constraint functional, we used Kreisselmeier-Steinhauser functional of the frequency processing stress or strain. For reshaping, we employed the traction method to keep the smoothness of original boundary. To reduce computational time, we used many PC clusters for analysis about actual loading history. By our approach, we obtained about 8% weight reduction of a suspension part while keeping the maximum value of the frequency processing stress or strain constant.