Language and human are not anything in the outside of nature. Not only babies, even adults can acquire new language naturally, if they have a natural multilingual environment around them. The reason it is possible would be that any human has an ability to grasp the whole of language, and at the same time, language has an order which is the easiest to acquire for humans. The process of this natural acquisition and a result of investigating the order of Japanese vowels are introduced. ©2000 American Institute of Physics.