For natural language understanding, it is essential to reveal semantic relations between words. To date, only the IS-A relation has been publicly available. Toward deeper natural language understanding, we semiautomatically constructed the domain dictionary that represents the domain relation between Japanese fundamental words. This is the first Japanese domain resource that is fully available. Besides, our method does not require a document collection, which is indispensable for keyword extraction techniques but is hard to obtain. As a task-based evaluation, we performed blog categorization. Also, we developed a technique for estimating the domain of unknown words.