The invention presents a device and a method for entering a character string in which a dictionary is changed dynamically in accordance with the input situation of the user, and in which character strings that are generally suitable for the input situation of the user can be entered. When a character string is entered, the situation in which the character string is entered is acquired. In accordance with the acquired situation, a dictionary used for the generation of candidate character strings or a portion of such a dictionary are affirmed as a situation-optimized dictionary. Optimized output candidate character strings are generated and outputted in accordance with the situation from character strings that have been input using this situation-optimized dictionary, and when output candidate character strings are affirmed and outputted, the affirmed character strings are stored in the situation-optimized dictionary in accordance with the acquired situation.