It is said that the gait pattern between adults and children are different. An index easy to comprehend is often used, for example step length and step width. In this research, we reduced the dimension of gait by using PCA and represented gait in lower dimensional space. After that we evaluated changeof gait between child and adults. We revealed that the gait in children change linearly in lower dimensional space. However, gait in adults doesn't appear the extension of the line.