In Japanese, there are a large number of notational variants of words. This is because Japanese words are written in three kinds of characters: kanji (Chinese) characters, hiragara letters, and katakana letters. Japanese students study basic rules of Japanese writing in school for many years. However, it is difficult to learn which variant is suitable for a certain context in official, business, and technical documents because the rules have many exceptions. Previous Japanese writing support systems were not concerned with them sufficiently. This is because their main purposes were misspelling detection. Students often use variants which are not misspelling but unsuitable for the contexts in official, business, and technical documents. To solve this problem, we developed a context sensitive variant dictionary. A writing support system based on the context sensitive variant dictionary detects unsuitable variants for the contexts in students' reports and shows suitable ones to the students. In this study, we first show how to develop a context sensitive variant dictionary by which our system determines which variant is suitable for a context in official, business, and technical documents. Finally, we conducted a control experiment and show the effectiveness of our dictionary.