When keywords are retrieved, speed and compactness are important. A trie is the data structure for keyword retrieval. Also, the double array is a key retrieval method by the trie and has speed and compactness. Some construction methods for the double array are proposed, but the problem is that construction time is exponentially late with large key set. To solve the problem, two methods to divide and construct the double array depending on depth are proposed. The proposed methods are confirmed to construct the double array fast.