Source criticism is very important on the research of architectural history as well as general history. In this point this research studied on the original form and change of Dokrak-dang that is very important building in architectural history of Korea. The result is as in the following. Dokrak-dang that Whoijae built at first was three by two kans size that had daecheong of four kans and ondol-bang of two kans. Gye-jeong that Whoijae built was three kans size that had daecheong of two kans and ondol-bang of one kan. After Whoijae died, Dokrak-dang’s ondol-bang was changed to maru between 1555 and 1556 and ondol-bang in west side and stack room was added in 1630. Gye-jeong was changed to ㄱ-shaped floor plan that was added up two kans from three kan’s ‘一’-shaped one.