The objective of this paper is to find out the costume in the era of Practical Science through the books written by Yack-Young Chung. Conclusions are described as follows: 1. A disorder of a class system is to be seen from the correlation between the upper class costume and the lower class costume. 2. He made an effort to develope technics and enlarge the specialist for the revolution of costume system. 3. He stressed the thrift for the revolution of custom through clothing. 4. He insisted that the use of clothing be out of formal courtesy, from the fact he showed his idea for the basic courtesy.