Katakana, Japanese phonogram mainly used for loan words, is a troublemaker in Japanese word segmentation. Since Katakana words are heavily domain-dependent and there are many Katakana neologisms, it is almost impossible to construct and maintain Katakana word dictionary by hand. This paper proposes an automatic segmentation method of Japanese Katakana compounds, which makes it possible to construct precise and concise Katakana word dictionary automatically, given only a medium or large size of Japanese corpus of some domain.