17. The apparatus of claim 15 , wherein the controller is configured to: determine the cost of the insert operation, delete operation, and replace operation corresponding to the identified keypad type by identifying at least one or more incorrect input types of high frequency of occurrence in the identified keypad type and, if operating conditions of at least one or more incorrect input types having the high frequency of occurrence are met, determining the cost of the insert operation, the delete operation or the replace operation as a first value and otherwise, determine the cost of the insert operation, the delete operation or the replace operation as a second value higher than the first value, and determine the cost of the insert operation, the delete operation or the replace operation as a basic cost whether the operating conditions are met or not.
15. The apparatus of claim 12 , wherein, the controller is configured to calculate the edit distance using the operations according to the respective cost by converting the input character string and the searched candidate words into key input strings of the identified keypad type and calculate an edit distance between the key input string of the input character string and the key input string of each of the searched candidate words.