This paper proposes an automatic method of gradually constructing case frames. First, a large raw corpus is parsed, and initial case frames are constructed from reliable predicate-argument examples in the parsing results.Second, case analysis based on the initial case frames is applied to the large corpus, and the case frames are upgraded by incorporating newly acquired information.Case frames are gradually fertilized in this way.We constructed case frames from news paper articles of 26 years, consisting of 26M sentences.The case frames are evaluated by hand, and furthermore evaluated through syntactic and case analysis.These results presented the effectiveness of the constructed case frames.