In this chapter, I survey the frequency distribution of commonly used words across different texts in Japanese. Using the Balanced Corpus of Contemporary Written Japanese, we examined the distribution. The results show the following. (1) The distribution draws a curve similar to Zipf’s law, but the curve always begins to increase shortly before the degree of commonality reaches its maximum, (2) neither the length nor the number of the texts affects the distribution trend, (3) as the text length increases, the number of commonly used words also increases linearly, but it reaches a maximum point due to the limited number of basic words.