In Japanese, case structure analysis is very important to handle several troublesome characteristics of Japanese such as scrambling, omission of case components, and disappearance of case markers. However, for lack of a widecoverage case frame dictionary, it has been difficult to perform case structure analysis accurately. Although several methods to construct a case frame dictionary from analyzed corpora have been proposed, they cannot avoid data sparseness problem. This paper proposes an unsupervised method of constructing a case frame dictionary from an enormous raw corpus by using a robust and accurate parser. It also provides a case structure analysis method based on the constructed dictionary.