This paper examines the usage of Japanese synonymous adverbs ‘Nanise’ and ‘Nanisiro’ while comparing the two adverbs from a diachronic point of view, the semantic features that arise from the word components, the syntactic appearance positions (Sentence-Initial and non Sentence-Initial) and co-occurrence expressions (‘desire to perform the action’, ‘denoting cause and reason’, ‘statement of the current situation’). (i) ‘Nanise’ and ‘Nanisiro’ are both words because the imperative form of the verb ‘su (ru) ’ (‘se (yo / i) ’ and ‘shiro’) is connected to an indefinite word (‘Nani’). From the beginning when the stand-alone form of was formed, it had no meaning of an imperative, and expressed the meaning of the reverse connection assumption (‘in any case’) . From the latter half of the early modern period (18C), the adverbial usage of ‘Nanise’ and ‘Nanisiro’ began to be seen, but it became more common after the Meiji era. ‘Nanise’ and ‘Nanisiro’ appeared at the beginning of the sentence at the syntactical appearance position, used in the same usage as the Modern Japanese(‘denoting cause and reason(with Kara) ’ and ‘statement of the current situation’). In some cases, ‘Nanisiro’ expressed desire to perform the action, showing characteristics different from the usage of Modern Japanese. (ⅱ)Although the use of both words has increased in the modern era, only a few cases of ‘Nanise’ have been seen from the Taisho period materials (after 1917) compared to ‘Nanishiro’, which has been used frequently since the early Meiji era. In addition, the use of ‘Nanise’ was particularly noticeable in materials written in the Kansai dialect, in which ‘Nanise’ was superior to ‘Nanise’, which was widely used throughout modern times. It is inferred that the tendency to use ‘Nanise’ and ‘Nanisiro’ in such modern materials is parallel to the east-west difference in the distribution of the two imperative forms of the verb ‘su(ru) ’. (ⅲ)In the distribution of usage, since modern times, the usage examples of ‘denoting cause and reason(with Kara)’ and ‘statement of the current situation’ have become more prominent in both, leading to the current usage. ‘Nanisiro’ was used in the example of ‘desire to perform the action’ from the early modern period to the modern era, but it is rarely used in Modern Japanese. In terms of writing style, most of ‘Nanise’ and ‘Nanisiro’ are used in spoken sentences and conversational sentences, and the tendency to use both as informal words has reached Modern Japanese.